Method for photocatalytically rendering a surface of a substrate superhydrophilic, a substrate with a superhydrophilic photocatalytic surface, and method of making thereof

ABSTRACT

The surface of a substrate is coated with an abrasion-resistant photocatalytic coating comprised of a semiconductor photocatalyst. Upon irradiation by a light having a wavelength of an energy higher than the bandgap energy of the photocatalyst, water is chemisorbed onto the surface in the form of hydroxyl groups (OH − ) whereby the surface of the photocatalytic coating is rendered highly hydrophilic. In certain embodiments, the surface of a mirror, lens, or windowpane is coated with the photocatalytic coating to exhibit a high degree of antifogging function. In another embodiment, an article or product coated with the photocatalytic coating is disposed outdoors and the highly hydrophilic surface thereof is self-cleaned as it is subjected to rainfall. In a still another embodiment, an article is coated with the photocatalytic coating and, when the article is soaked in, rinsed by or wetted with water, fatty dirt and contaminants are readily released without resort to a detergent.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates broadly to the art of rendering andmaintaining a surface of a substrate highly hydrophilic. Moreparticularly, the present invention relates to the antifogging artwherein the surface of a transparent substrate such as a mirror, lensand sheet glass is made highly hydrophilic to thereby prevent fogging ofthe substrate or formation of water droplets. This invention is alsoconcerned with the art wherein the surface of a building, windowpane,machinery or article is rendered highly hydrophilic in order to preventfouling of, to permit self-cleaning of or to facilitate cleaning of thesurface. This invention also relates to a hydrophilifiable member havinga surface layer which is capable of having an extremely small contactangle with water, a method for rendering the member hydrophilic, amethod for forming a hydrophilifiable surface layer, and a coatingcomposition for forming a hydrophilifiable surface layer.

[0003] 2. Description of the Prior Art

[0004] It is often experienced that, in the cold seasons, windshieldsand window-glasses of automobiles and other vehicles, windowpanes ofbuildings, lenses of eyeglasses, and cover glasses of variousinstruments are fogged by moisture condensate. Similarly, in a bathroomor lavatory, it is often encountered that mirrors and eyeglass lensesare fogged by steam.

[0005] Fogging of the surface of an article results from the fact that,when the surface is held at a temperature lower than the dew point ofthe ambient atmosphere, condensation of moisture in the ambient airtakes place to form moisture condensate at the surface.

[0006] If the condensate particles are sufficiently fine and small sothat the diameter thereof is on the order of one half of the wavelengthof the visible light, the particles cause scattering of light wherebywindow-glasses and mirrors become apparently opaque thereby giving riseto a loss of visibility.

[0007] When condensation of moisture further proceeds so that finecondensate particles are merged together to grow into discrete largerdroplets, the refraction of light taking place at the interface betweenthe droplets and the surface and between the droplets and the ambientair causes the surface to be blurred, dimmed, mottled, or clouded. As aresult, an image viewed through a transparent article such as sheetglass may become distorted, or the reflected image in a mirror may bedisturbed.

[0008] Similarly, when windshields and window-glasses of vehicles,windowpanes of buildings, rearview mirrors of vehicles, lenses ofeyeglasses, or shields of masks or helmets are subjected to rain orwater splash so that discrete water droplets are adhered to the surface,their surface is blurred, dimmed, mottled, or clouded, resulting in theloss of visibility.

[0009] The term “antifogging” as used herein and in the appended claimsis intended to mean broadly the art of preventing or minimizingoccurrence of optical trouble resulting from fogging, growth ofcondensate droplets or adherent water droplets mentioned above.

[0010] The antifogging art can significantly affect safety andefficiency in a variety of setting. For example, the safety of vehiclesand traffic can be undermined if the windshields, window-glasses orrearview mirrors of vehicles are fogged or blurred. Fogging ofendoscopic lenses and dental mouth mirrors may hinder proper andaccurate diagnosis, operation and treatment. If cover glasses ofmeasuring instruments are fogged, a reading of data will becomedifficult.

[0011] The windshields of automobiles and other vehicles are normallyprovided with windshield wipers, defrosting devices and heaters so as toavoid visibility problems, which arise particularly in the cold seasonsand under rainy conditions. However, it is not commercially feasible toinstall this equipment on the side windows of a vehicle, or on therearview mirrors arranged outside of the vehicle. Similarly, it isdifficult, if possible at all, to mount such antifogging equipment onwindowpanes of buildings, lenses of eyeglasses and endoscopes, dentalmouth mirrors, shields of masks and helmets, or cover glasses ofmeasuring instruments.

[0012] As is well-known, a simple and convenient antifogging methodconventionally used in the art is to apply onto a surface an antifoggingcomposition containing either a hydrophilic compound such aspolyethylene glycol or a hydrophobic or water-repellent compound such assilicone. However, the disadvantage of this method is that theantifogging coating thus formed is only temporary in nature and isreadily removed when rubbed or washed with water so that itseffectiveness is prematurely lost.

[0013] Japanese Utility Model Kokai Publication No. 3-129357 (MitsubishiRayon) discloses an antifogging method for a mirror wherein the surfaceof a substrate is provided with a polymer layer and the layer issubjected to irradiation by ultraviolet light, followed by treatmentwith an aqueous alkaline solution to thereby form acid radicals at ahigh density whereby the surface of the polymer layer is renderedhydrophilic. Again, however, it is believed that, according to thismethod, the hydrophilic property of the surface is degraded as timeelapses because of adherent contaminants so that the antifoggingfunction is lost over time.

[0014] Japanese Utility Model Kokai Publication No. 5-68006 (StanleyElectric) discloses an antifogging film made of a graftcopolymer of anacrylic monomer having hydrophilic groups and a monomer havinghydrophobic groups. The graftcopolymer is described as having a contactangle with water of about 50°. It is therefore believed that thisantifogging film does not exhibit a sufficient antifogging capability.

[0015] Isao Kaetsu “Antifogging Coating Techniques for Glass”, Moderncoating Techniques, pages 237-249, published by Sogo Gijutsu Center(1986), describes various antifogging techniques used in the prior art.The author Mr. Kaetsu nevertheless reports that the prior artantifogging techniques, which consist of rendering a surfacehydrophilic, suffer from significant problems which must be overcome inreducing them to practice, and, further reports that the conventionalantifogging coating techniques seemingly come up against a barrier.

[0016] Accordingly, an object of the invention is to provide anantifogging method which is capable of realizing a high degree ofvisibility in a transparent substrate such as a mirror, lens or glass.

[0017] Another object of the invention is to provide an antifoggingmethod wherein the surface of a transparent substrate such as a mirror,lens or glass is maintained highly hydrophilic for an extended period oftime.

[0018] Still another object of the invention is to provide anantifogging method wherein the surface of a transparent substrate suchas a mirror, lens and glass is almost permanently maintained highlyhydrophilic.

[0019] A further object of the invention is to provide an antifoggingcoating which has an improved durability and abrasion resistance.

[0020] Another object of the invention is to provide an antifoggingcoating which can be readily applied onto a surface requiringantifogging treatment.

[0021] Yet another object of the invention is to provide an antifoggingtransparent substrate such as a mirror, lens or glass, as well as amethod of making such an antifogging transparent substrate, wherein thesubstrate surface is maintained highly hydrophilic for an extendedperiod of time to thereby provide a high degree of antifogging propertyfor an extended period.

[0022] In the fields of architecture and painting, it has been pointedout that growing environmental pollution tends to inadvertentlyaccelerate fouling, contamination or soiling of exterior buildingmaterials, including outdoor buildings themselves and the coatingsthereon.

[0023] In this regard, air-borne grime and dust particles are allowedunder fair weather conditions to fall and deposit on roofs and outerwalls of buildings. When it rains, the deposits are washed away byrainwater and are caused to flow along the outer walls of the buildings.Furthermore, air-borne grime is captured by rain and is carried ontosurfaces (such as outer walls) of outdoor structures and buildings,where the grime may flow along or down the surface. For these reasons,contaminant substances are caused to adhere onto the surface along thepaths of rainwater. As the surface is dried, a striped pattern of dirt,stain or smudge will appear on the surface.

[0024] The dirt or stain thus formed on the exterior building materialsand exterior coatings consists of contaminant substances which includecombustion products such as carbon black, city grime, and inorganicsubstances such as clay particles. The diversity of the foulingsubstances is considered to make the antifouling countermeasurescomplicated (Yoshinori KITSUTAKA, “Accelerated Test Method For soilingon Finishing Materials of External Walls”, Bulletin of JapanArchitecture Society, vol. 404 (October 1989), pages 15-24).

[0025] Hitherto, it has been commonly considered in the art thatwater-repellent paints such as those containing polytetrafluoroethylene(PTFE) are desirable to prevent fouling or soiling of exterior buildingmaterials and the like. Recently, however, it is pointed out that, inorder to cope with city grime containing a large amount of oleophiliccomponents, it is rather desirable to render the surface of coatings ashydrophilic as possible (“Highpolymer”, vol. 44, May 1995, page 307).

[0026] Accordingly, it has been proposed in the art to coat a buildingwith a hydrophilic graftcopolymer (Newspaper “Daily Chemical Industry”,January 30, 1995). Reportedly, the coating film presents ahydrophilicity of 30-40% in terms of the contact angle with water.

[0027] However, in view of the fact that inorganic dusts, which maytypically be represented by clay minerals, have a contact angle withwater ranging from 20° to 50° (so that they have affinity forgraftcopolymer having a contact angle with water of 30-40° ), it isconsidered that such inorganic dusts are apt to adhere to the surface ofthe graftcopolymer coating and, hence, the coating is not able toprevent fouling or contamination by inorganic dusts.

[0028] Also available in the market are various hydrophilic paints whichcomprise acrylic resin, acryl-silicone resin, aqueous silicone, blockcopolymers of silicone resin and acrylic resin, acryl-styrene resin,ethylene oxides of sorbitan fatty acid, esters of sorbitan fatty acid,acetates of urethane, cross-linked urethane of polycarbonatediol and/orpolyisocyanate, or cross-linked polymers of alkylester polyacrylate.However, since the contact angle with water of these hydrophilic paintsis as large as 50-70°, they are not suitable to effectively preventfouling by city grimes which contain large amount of oleophiliccomponents.

[0029] Accordingly, a further object of the invention is to provide amethod for rendering a surface of a substrate highly hydrophilic andantifouling.

[0030] Another object of the invention is to provide a method whereinthe surface of buildings, window glasses, machinery or articles isrendered highly hydrophilic to thereby prevent fouling of or to permitself-cleaning of or to facilitate cleaning of the surface.

[0031] Yet another object of the invention is to provide a highlyhydrophilic antifouling substrate, as well as a method of makingthereof, which is adapted to prevent fouling of or to permitself-cleaning of or to facilitate cleaning of the surface.

[0032] In certain apparatus, formation of moisture condensate on asurface thereof often hampers operation of the apparatus when condensatehas grown into droplets. In heat exchangers, for example, the heatexchanging efficiency would be lowered if condensate particles adheringto radiator fins have grown into large droplets.

[0033] Accordingly, another object of the invention is to provide amethod for preventing adherent moisture condensate from growing intolarger water droplets wherein a surface is made highly hydrophilic tothereby permit adherent moisture condensate to spread into a water film.

DISCLOSURE OF THE INVENTION

[0034] The present inventors have found that, upon photoexcitation, asurface of a photocatalyst is rendered highly hydrophilic. Surprisingly,it has been discovered that, upon photoexcitation of photocatalytictitania with ultraviolet light, the surface thereof is rendered highlyhydrophilic to the degree that the contact angle with water becomes lessthan 10°, more particularly less than 5°, and even reached about 0°.

[0035] Based on the foregoing findings, the present invention provides,broadly, a method for rendering a surface of a substrate highlyhydrophilic, a substrate having a highly hydrophilic surface and amethod of making such a substrate. According to the invention, thesurface of the substrate is coated with an abrasion-resistantphotocatalytic coating comprised of a photocatalytic semiconductormaterial.

[0036] Upon irradiation for a sufficient time with a sufficientintensity of a light having a wavelength which has an energy higher thanthe bandgap energy of the photocatalytic semiconductor, the surface ofthe photocatalytic coating is rendered highly hydrophilic to exhibit asuper-hydrophilicity. The term “super-hydrophilicity” or“super-hydrophilic” as used herein refers to a highly hydrophilicproperty (i.e., water wettability) of less than about 10° in terms ofthe contact angle with water. Similarly, the term“superhydrophilification” or “superhydrophilify” refers to rendering asurface highly hydrophilic to the degree that the contact angle withwater becomes less than about 10°. It is preferred that asuperhydrophilic surface have a water wettability of less than about 5°.

[0037] The process of superhydrophilification of a surface resultingfrom photoexcitation of a photocatalyst cannot be explained presentlywith any certainty. Seemingly, photocatalytic superhydrophilification isnot necessarily identical with photodecomposition of a substance arisingfrom photocatalytic redox process known hitherto in the field ofphotocatalyst. In this regard, the conventional theory admitted in theart regarding the photocatalytic redox process was that electron-holepairs are generated upon photoexcitation of the photocatalyst, theelectrons thus generated acting to reduce the surface oxygen to producesuperoxide ions (O₂ ⁻), the holes acting to oxidize the surface hydroxylgroups to produce hydroxyl radicals (.OH), these highly active oxygenspecies (O₂ ⁻ and .OH) then acting to decompose a substance throughredox process.

[0038] However, it seems that the superhydrophilification phenomenonprovoked by a photocatalyst is not consistent, in at least two aspects,with the conventional understanding and observation regarding thephotocatalytic decomposition process of substances. First, according toa theory widely accepted hitherto, it has been believed that, in acertain photocatalyst such as rutile and tin oxide, the energy level ofthe conduction band is not high enough to promote the reduction processso that the electrons photoexcited up to the conduction band remainunused and become excessive whereby the electron-hole pairs oncegenerated by photoexcitation undergo recombination without contributingin the redox process. In contrast, the present inventors have observedthat the superhydrophilification process by a photocatalyst takes placeeven with rutile and tin oxide, as described later.

[0039] Secondly, the conventional wisdom was that the decomposition ofsubstances due to photocatalytic redox process is not developed unlessthe thickness of a photocatalytic layer is greater than at least 100 nm.Conversely, the present inventors have found that photocatalyticsuperhydrophilification occurs even with a photocatalytic coating havinga thickness on the order of several nanometers.

[0040] Accordingly, it is believed (though it cannot be confirmed withcertainty) that the superhydrophilification process caused by aphotocatalyst is a phenomenon somewhat different from photodecompositionof substances resulting from the photocatalytic redox process. Asdescribed later, it has been observed that superhydrophilification of asurface does not occur unless a light having an energy higher than theband gap energy of the photocatalyst is irradiated. It is consideredthat, presumably, the surface of a photocatalytic coating is renderedsuperhydrophilic as a result of water being chemisorbed thereon in theform of hydroxyl groups (OH⁻) under the photocatalytic action of thephotocatalyst.

[0041] Once the surface of the photocatalytic coating has been madehighly hydrophilic upon photoexcitation of the photocatalyst, thehydrophilicity of the surface will be sustained for a certain period oftime even if the substrate is placed in the dark. As time elapses, thesuperhydrophilicity of the surface will be gradually lost because ofcontaminants adsorbed on the surface hydroxyl groups. However, thesuperhydrophilicity will be restored when the surface is again subjectedto photoexcitation.

[0042] To initially superhydrophilify the photocatalytic coating, anysuitable source of light may be used which has a wavelength of an energyhigher than the band gap energy of the photocatalyst. In the case ofthose photocatalysts such as titania for which the photoexcitingwavelength is in the ultraviolet range of the spectrum, the ultravioletlight contained in the sunlight may advantageously be used as thephotoexciting light source if the sunlight impinges upon the substratecoated by the photocatalytic coating. When the photocatalyst is to bephotoexcited indoors or at night, an artificial light source may beused. In the case where the photocatalytic coating is made of silicablended titania as described later, the surface thereof can readily berendered hydrophilic even by a weak ultraviolet radiation contained inthe light emitted from a fluorescent lamp.

[0043] After the surface of the photocatalytic coating has once beensuperhydrophilified, the superhydrophilicity may be maintained orrenewed by a relatively weak light. In the case of titania, for example,maintenance and restoration of the superhydrophilicity may beaccomplished to a satisfactory degree even by a weak ultraviolet lightcontained in the light of indoor illumination lamps such as fluorescentlamps.

[0044] The photocatalytic coating of the present invention exhibitssuper-hydrophilicity even if the thickness thereof is made extremelysmall. It presents a sufficient hardness when made, in particular, froma photocatalytic semiconductor material comprising a metal oxide.Therefore, the present photocatalytic coating may have an adequatedurability and abrasion resistivity.

[0045] Superhydrophilification of a surface may be utilized for variousapplications. In one aspect of the invention, this invention provides anantifogging method for a transparent member, or provides an antifoggingtransparent member, or provides a method of making an antifoggingmember. According to the invention, a transparent member is prepared,and the surface of the transparent member is coated with aphotocatalytic coating.

[0046] The transparent member may include a mirror such as a rearviewmirror for a vehicle, a bathroom or lavatory mirror, a dental mouthmirror, or a road mirror; a lens such as an eyeglass lens, optical lens,photographic lens, endoscopic lens, or light projecting lens; a prism; awindowpane for a building or control tower; a windowpane for a vehiclesuch as an automobile, railway vehicle, aircraft, watercraft, submarine,snowmobile, ropeway gondola, pleasure garden gondola and spacecraft; awindshield for a vehicle such as an automobile, railway vehicle,aircraft, watercraft, submarine, snowmobile, motorcycle, ropewaygondola, pleasure garden gondola and spacecraft; a shield for protectiveor sporting goggles or mask including diving mask; a shield for ahelmet; a show window glass for chilled foods; or a cover glass for ameasuring instrument.

[0047] Upon subjecting the transparent member provided with thephotocatalytic coating to irradiation by a light to thereby photoexcitethe photocatalyst, the surface of the photocatalytic coating will besuperhydrophilified. Thereafter, in the event that moisture in the airor steam undergoes condensation, the condensate will be transformed intoa relatively uniform film of water without forming discrete waterdroplets. As a result, the surface will be free from the formation of alight diffusing fog.

[0048] Similarly, in the event that a windowpane, a rearview mirror of avehicle, a windshield of a vehicle, eyeglass lenses, a helmet shield, orother substrate is subjected to a rainfall or a splash of water, thewater droplets adhering onto the surface will be quickly spread overinto a uniform water film thereby preventing formation of discrete waterdroplets which would otherwise hinder visibility through, or reflectionfrom, the substrate.

[0049] Accordingly, a high degree of view and visibility is secured sothat the safety of vehicle and traffic is secured and the efficiency ofvarious activities improved.

[0050] In another aspect, this invention provides a method forself-cleaning a surface of a substrate wherein the surface issuperhydrophilified and is self-cleaned by rainfall. This invention alsoprovides a self-cleaning substrate and a method of making thereof.

[0051] The substrate may be any of a variety of articles, including anexterior member, window sash, structural member, or windowpane of abuilding; an exterior member or coating of a vehicle such as automobile,railway vehicle, aircraft, and watercraft; an exterior member, dustcover or coating of a machine, apparatus or article; and an exteriormember or coating of a traffic sign, various display devices, andadvertisement towers, that are made, for example, of metal, ceramics,glass, plastics, wood, stone, cement, concrete, a combination thereof, alaminate thereof, or other materials. The surface of the substrate iscoated with the photocatalytic coating.

[0052] Since the building, or machine or article disposed outdoors, isexposed to the sunlight during the daytime, the surface of thephotocatalytic coating will be rendered highly hydrophilic. Furthermore,the surface will occasionally be subjected to rainfall. Each time thesuperhydrophilified surface receives a rainfall, dust and grime andcontaminants deposited on the surface of the substrate will be washedaway by rain whereby the surface is self-cleaned.

[0053] As the surface of the photocatalytic coating is rendered highlyhydrophilic to the degree that the contact angle with water becomes lessthan about 10°, preferably less than about 5°, particularly equal toabout 0°, not only city grime containing large amounts of oleophilicconstituents but also inorganic dusts such as clay minerals will bereadily washed away from the surface. In this manner, the surface of thesubstrate will be self-cleaned and kept clean to a high degree under theaction of nature. This will permit, for instance, to eliminate orlargely reduce cleaning of windowpanes of towering buildings.

[0054] In still another aspect, this invention provides an antifoulingmethod for a building, window glass, machine, apparatus, or articlewherein the surface thereof is provided with a photocatalytic coatingand is rendered highly hydrophilic to prevent fouling.

[0055] The surface thus superhydrophilified will prevent contaminantsfrom adhering to the surface when rainwater which is laden withcontaminants originating from air-borne dust and grime flows down alongthe surface. Therefore, in combination with the above-mentionedself-cleaning function performed by rainfall, the surface of thebuilding and the like may be maintained in a high degree of cleanlinessfor an extremely long period of time.

[0056] In a further aspect of the invention, a photocatalytic coating isprovided on a surface of an apparatus or article, such as an exterior orinterior member of a building, or a windowpane, household, toilet bowl,bath tub, wash basin, lighting fixture, kitchenware, tableware, sink,cooking range, kitchen hood, or ventilation fan, said apparatus orarticle being made from metal, ceramics, glass, plastics, wood, stone,cement, concrete, a combination thereof, a laminate thereof, or othermaterials, and the surface is photoexcited as required.

[0057] When these articles which are fouled by oil or fat are soaked in,wetted with or rinsed by water, fatty dirt and contaminants will bereleased from the superhydrophilified surface of the photocatalyticcoating and will be readily removed therefrom. Accordingly, for example,a tableware fouled by oil or fat may be cleansed without resort to adetergent.

[0058] In another aspect, this invention provides a method forpreventing growth of condensate droplets adhering to a substrate or forcausing adherent water droplets to spread into a uniform water film. Tothis end, the surface of the substrate is coated with a photocatalyticcoating.

[0059] Once the surface of the substrate has been superhydrophilifiedupon photoexcitation of the photocatalytic coating, moisture condensateor water droplets that have come to adhere to the surface will be spreadover the surface to form a uniform aqueous film. By applying thismethod, for example, to radiator fins of a heat exchanger, it ispossible to prevent fluid passages for a heat exchange medium from beingclogged by condensate; thus the present invention may be used to enhancethe heat exchange efficiency. Also, when this method is applied to amirror, lens, windowpane, windshield, pavement, or other such surface,it is possible to promote drying of the surface after wetting withwater.

[0060] The present inventors have further discovered thathydrophilification of a surface layer made of a photocatalyst resultsfrom water molecules being physisorbed onto the surface under thephotocatalytic action of the photocatalyst.

[0061] Based on this discovery, the present invention further provides amethod and a composite wherein a substrate is coated with a surfacelayer comprised of a photocatalyst and wherein upon photoexcitation ofthe photocatalyst the molecules of water are physisorbed by hydrogenbonding onto the surface layer to thereby form a layer of physisorbedwater of a high density.

[0062] As a layer of physisorbed water is formed on the surface of thephotocatalytic layer, the surface is readily hydrophilified to a highdegree. Due to the presence of the layer of physisorbed water, thehydrophilicity of the surface is maintained for a long period of timeeven after photoexcitation is discontinued, thereby minimizing the lossof hydrophilicity over time. Moreover, when the photocatalyst isphotoexcited again, the hydrophilicity of the surface is readilyrecovered within a short period of time of irradiation or with a weakirradiation intensity.

[0063] These features and advantages of the invention as well as otherfeatures and advantages thereof will become apparent from the followingdescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0064]FIG. 1 shows the energy level of the valance band and theconduction band of various semiconductor photocatalysts usable in thepresent invention;

[0065]FIGS. 2A and 2B are schematic cross-sectional views in amicroscopically enlarged scale of the photocatalytic coating formed onthe surface of a substrate and showing the hydroxyl groups beingchemisorbed on the surface upon photoexcitation of the photocatalyst;

[0066] FIGS. 3-5, 7 and 9 are graphs respectively showing the variation,in response to time, of the contact angle with water of variousspecimens in the Examples as the specimens are subjected to irradiationof ultraviolet light;

[0067]FIG. 6 shows Raman spectra of a surface of photocatalytic coatingmade of silicone;

[0068]FIGS. 8 and 16 are graphs showing the result of pencil hardnesstests;

[0069]FIG. 10 is a graph showing the relationship between the thicknessof the photocatalytic coating and the capability of the coating todecompose methyl mercaptan;

[0070]FIGS. 11A and 11B are front and side elevational views,respectively, of outdoor accelerated fouling testing equipment;

[0071] FIGS. 12-15 are graphs showing the contact angle with waterversus the molar ratio of silica in silica-blended titania;

[0072]FIG. 17 is a graph showing to what degree various surfaces havingdifferent hydrophilicity are fouled by city grime and sludge;

[0073] FIGS. 18A-18C are graphs showing the variation, in response totime, of the contact angle with water when ultraviolet light havingdifferent wavelengths is irradiated on the surface of the photocatalyticcoating;

[0074]FIGS. 19A and 19B, FIGS. 20A and 20B, FIGS. 21A and 21B, FIGS. 22Aand 22B, and FIGS. 23A and 23B, respectively, are graphs showing theinfrared absorption spectrum of the surface of the photocatalyticcoating; and,

[0075]FIG. 24 is a schematic cross-sectional view in a microscopicallyenlarged scale of the surface of the photocatalytic coating and showingmolecules of water physisorped onto the surface upon photoexcitation ofthe photocatalyst.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0076] A substrate having a surface requiring superhydrophilification isprepared and is coated with a photocatalytic coating. In the case wherethe substrate is made from a heat resistive material such as metal,ceramics and glass, the photocatalytic coating may be fixed on thesurface of the substrate by sintering particles of a photocatalyst asdescribed later. Alternatively, a thin film of the amorphous form of aprecursor of the photocatalyst may be first formed on the surface of thesubstrate and the amorphous photocatalyst precursor may then betransformed into photoactive photocatalyst by heating andcrystallization.

[0077] In the case where the substrate is formed of a non heat-resistivematerial such as plastic or is coated with a paint, the photocatalyticcoating may be formed by applying onto the surface aphotooxidation-resistant coating composition containing thephotocatalyst and by curing the coating composition, as described later.

[0078] When an antifogging mirror is to be manufactured, a reflectivecoating may be first formed on the substrate and the photocatalyticcoating may then be formed on the front surface of the mirror.Alternatively, the reflective coating may be formed on the substratesubsequent to or during the course of the step of coating of thephotocatalyst.

Photocatalyst

[0079] The most preferred example of the photocatalyst usable in thephotocatalytic coating according to the invention is titania (TiO₂).Titania is harmless, chemically stable and available at a low cost.Furthermore, titania has a high band gap energy and, hence, requiresultraviolet (UV) light for photoexcitation. This means that absorptionof the visible light does not occur during the course of photoexcitationso that the coating is free from the problem of coloring which wouldotherwise occur due to a complementary color component. Accordingly,titania is particularly suitable to coat on a transparent member such asglass, lens and mirror.

[0080] Both the anatase and rutile forms of titania may be used. Theadvantage of the anatase form of titania is that a sol in whichextremely fine particles of anatase are dispersed is readily availableon the market so that it is easy to make an extremely thin film. On theother hand, the advantage of the rutile form of titania is that it canbe sintered at a high temperature so that a coating that has excellentstrength and abrasion resistance can be obtained. Although the rutileform of titania is lower in the conduction band level than the anataseform as shown in FIG. 1, it may be used as well for the purpose ofphotocatalytic superhydrophilification.

[0081] It is believed that, when a substrate 10 is coated with aphotocatalytic coating 12 of titania and the coating is subjected tophotoexcitation by UV light, water is chemisorbed on the surface in theform of hydroxyl groups (OH⁻) as a result of the photocatalytic action,as shown in FIG. 2A. As a result, the surface becomes superhydrophilic.

[0082] Other photocatalysts which can be used in the photocatalyticcoating according to the invention may include a metal oxide such asZnO, SnO₂, SrTiO₃, WO₃, Bi₂O₃, or Fe₂O₃, as shown in FIG. 1. It isbelieved that, similar to titania, these metal oxides are apt to adsorbthe surface hydroxyl groups (OH⁻) because the metallic element andoxygen are present at the surface.

[0083] As shown in FIG. 2B, the photocatalytic coating may be formed byblending particles 14 of photocatalyst in a layer 16 of metal oxide. Inparticular, the surface can be hydrophilified to a high degree whensilica or tin oxide is blended in the photocatalyst as described later.

Thickness of Photocatalytic Coating

[0084] In the case that the substrate is made of a transparent materialas in the case of glass, a lens and a mirror, it is preferable that thethickness of the photocatalytic coating is not greater than 0.2 μm. Withsuch a thickness, coloring of the photocatalytic coating due to theinterference of light can be avoided. Moreover, the thinner thephotocatalytic coating is, the more transparent the substrate can be. Inaddition, the abrasion resistance of the photocatalytic coating isincreased with decreasing thickness.

[0085] The surface of the photocatalytic coating may be covered furtherby an abrasion-resistant or corrosion-resistant protective layer orother functional film which is susceptible to hydrophilification.

Formation of Photocatalytic Layer by Calcination of Amorphous Titania

[0086] When the substrate is made of a heat resistive material such asmetal, ceramics and glass, one of the preferred methods for forming anabrasion resistant photocatalytic coating which exhibits thesuperhydrophilicity of such a degree that the contact angle with waterbecomes as small as 0° is to first form a coating of the amorphous formof titania on the surface of the substrate and to then calcine thesubstrate to thereby transform by phase transition amorphous titaniainto crystalline titania (i.e., anatase or rutile). Formation ofamorphous titania may be carried out by one of the following methods.

[0087] (1) Hydrolysis and Dehydration Polymerization of Organic TitaniumCompound

[0088] To an alkoxide of titanium, such as tetraethoxytitanium,tetraisopropoxytitanium, tetra-n-propoxytitanium, tetrabuthoxytitanium,or tetramethoxytitanium, is added a hydrolysis inhibitor such ashydrochloric acid and ethylamine, the mixture being diluted by alcoholsuch as ethanol or propanol. While subjected to partial or completehydrolysis, the mixture is applied to the surface of the substrate byspray coating, flow coating, spin coating, dip coating, roll coating orany other suitable coating method, followed by drying at a temperatureranging from the ambient temperature to 200° C. Upon drying, hydrolysisof titanium alkoxide will be completed to result in the formation oftitanium hydroxide which then undergoes dehydration polymerizationwhereby a layer of amorphous titania is formed on the surface of thesubstrate.

[0089] In lieu of titanium alkoxide, other organic compounds of titaniumsuch as chelate of titanium or acetate of titanium may be employed.

[0090] (2) Formation of Amorphous Titania from Inorganic TitaniumCompound

[0091] An acidic aqueous solution of an inorganic compound of titaniumsuch as TiCl₄ or Ti(SO₄)₂ is applied to the surface of a substrate byspray coating, flow coating, spin coating, dip coating, or roll coating.The substrate is then dried at a temperature of 100-200° C. to subjectthe inorganic compound of titanium to hydrolysis and dehydrationpolymerization to form a layer of amorphous titania on the surface ofthe substrate. Alternatively, amorphous titania may be formed on thesurface of the substrate by chemical vapor deposition of TiCl₄.

[0092] (3) Formation of Amorphous Titania by Sputtering

[0093] Amorphous titania may be deposited on the surface of thesubstrate by bombarding a target of metallic titanium with an electronbeam in an oxidizing atmosphere.

[0094] (4) Calcination Temperature

[0095] Calcination of amorphous titania may be carried out at atemperature at least higher than the crystallization temperature ofanatase. Upon calcination at a temperature of 400-500° C. or more,amorphous titania may be transformed into the anatase form of titania.Upon calcination at a temperature of 600-700° C. or more, amorphoustitania may be transformed into the rutile form of titania.

[0096] (5) Formation of Diffusion Prevention Layer

[0097] When the substrate is made of materials such as glass or glazedtile which contains alkaline network-modifier ions (e.g., sodium), it ispreferable that an intermediate layer of silica and the like is formedbetween the substrate and the layer of amorphous titania prior tocalcination. This arrangement prevents alkaline network-modifier ionsfrom being diffused from the substrate into the photocatalytic coatingduring calcination of amorphous titania. As a result,superhydrophilification may be accomplished to the degree that thecontact angle with water becomes as small as 0°.

Photocatalytic Layer of Silica-blended Titania

[0098] Another preferred method of forming an abrasion resistantphotocatalytic coating which exhibits the superhydrophilicity of such adegree that the contact angle with water approaches or is equal to 0° isto form on the surface of the substrate a photocatalytic coatingcomprised of a mixture of titania and silica. The ratio of silica to thesum of titania and silica (by mole percent) may be 5-90%, preferably10-70%, more preferably 10-50%. The formation of a photocatalyticcoating comprised of silica-blended titania may be carried out by any ofthe following methods.

[0099] (1) A suspension containing particles of the anatase form orrutile form of titania and particles of silica is applied to the surfaceof a substrate, followed by sintering at a temperature less than thesoftening point of the substrate.

[0100] (2) A mixture of a precursor of amorphous silica (e.g.,tetraalkoxysilane such as tetraethoxysilane, tetraisopropoxysilane,tetra-n-propoxysilane, tetrabuthoxysilane, and tetramethoxysilane;silanol formed by hydrolysis of tetraalkoxysilane; or polysiloxanehaving a mean molecular weight of less than 3000) and a crystallinetitania sol is applied to the surface of a substrate and is subjected tohydrolysis where desired to form silanol, followed by heating at atemperature higher than about 100° C. to subject the silanol todehydration polymerization to thereby form a photocatalytic coatingwherein titania particles are bound by amorphous silica. In this regard,if dehydration polymerization of silanol is carried out at a temperaturehigher than about 200° C., polymerization of silanol is accomplished toa high degree so that the alkali resistance of the photocatalyticcoating is enhanced.

[0101] (3) A suspension comprised of particles of silica dispersed in asolution of a precursor of amorphous titania (e.g., an organic compoundof titanium such as alkoxide, chelate or acetate of titanium; or aninorganic compound of titanium such as TiCl₄ and Ti(SO₄)₂) is applied tothe surface of a substrate and then the precursor is subjected tohydrolysis and dehydration polymerization at a temperature ranging fromthe ambient temperature to 200° C. to thereby form a thin film ofamorphous titania wherein particles of silica are dispersed. Then, thethin film is heated at a temperature higher than the crystallizationtemperature of titania but lower than the softening point of thesubstrate to thereby transform amorphous titania into crystallinetitania by phase transition.

[0102] (4) Added to a solution of a precursor of amorphous titania(e.g., an organic compound of titanium such as an alkoxide, chelate oracetate of titanium; or an inorganic compound of titanium such as TiCl₄or Ti(SO₄)₂) is a precursor of amorphous silica (e.g., atetraalkoxysilane such as tetraethoxysilane, tetraisopropoxysilane,tetra-n-propoxysilane, tetrabuthoxysilane, or tetramethoxysilane; ahydrolyzate thereof, i.e., silanol; or a polysiloxane having a meanmolecular weight of less than 3000) and the mixture is applied to thesurface of a substrate. Then, these precursors are subjected tohydrolysis and dehydration polymerization to form a thin film made of amixture of amorphous titania and amorphous silica. Thereafter, the thinfilm is heated at a temperature higher than the crystallizationtemperature of titania but lower than the softening point of thesubstrate to thereby transform amorphous titania into crystallinetitania by phase transition.

Photocatalytic Layer of Tin Oxide-blended Titania

[0103] Still another preferred method of forming an abrasion resistantphotocatalytic coating which exhibits the superhydrophilicity of such adegree that the contact angle with water is equal to 0° is to form onthe surface of a substrate a photocatalytic coating comprised of amixture of titania and tin oxide. The ratio of tin oxide to the sum oftitania and tin oxide may be 1-95% by weight, preferably 1-50% byweight. Formation of a photocatalytic coating comprised of tinoxide-blended titania may be carried out by any of the followingmethods.

[0104] (1) A suspension containing particles of the anatase form orrutile form of titania and particles of tin oxide is applied to thesurface of a substrate, followed by sintering at a temperature less thanthe softening point of the substrate.

[0105] (2) A suspension comprised of particles of tin oxide dispersed ina solution of a precursor of amorphous titania (e.g., an organiccompound of titanium such as alkoxide, chelate or acetate of titanium;or an inorganic compound of titanium such as TiCl₄ or Ti(SO₄)₂) isapplied to the surface of a substrate and then the precursor issubjected to hydrolysis and dehydration polymerization at a temperatureranging from the ambient temperature to 200° C. to thereby form a thinfilm of amorphous titania wherein particles of tin oxide are dispersed.Then, the thin film is heated at a temperature higher than thecrystallization temperature of titania but lower than the softeningpoint of the substrate to thereby transform amorphous titania intocrystalline titania by phase transition.

Silicone Paint Containing Photocatalyst

[0106] A further preferred method of forming a photocatalytic coatingwhich exhibits the superhydrophilicity of such a degree that the contactangle with water is equal to 0° is to use a coating composition whereinparticles of a photocatalyst are dispersed in a film forming element ofuncured or partially cured silicone (organopolysiloxane) or a precursorthereof.

[0107] The coating composition is applied on the surface of a substrateand the film forming element is then subjected to curing. Uponphotoexcitation of the photocatalyst, the organic groups bonded to thesilicon atoms of the silicone molecules are substituted with hydroxylgroups under the photocatalytic action of the photocatalyst, asdescribed later with reference to Examples 13 and 14, whereby thesurface of the photocatalytic coating is superhydrophilified.

[0108] This method provides several advantages. Since thephotocatalyst-containing silicone paint can be cured at ambienttemperature or at a relatively low temperature, this method may beapplied to a substrate formed of a non-heat-resistant material such asplastics. The coating composition containing the photocatalyst may beapplied whenever desired by way of brush painting, spray coating, rollcoating and the like on any existing substrate requiringsuperhydrophilification of the surface. Superhydrophilification byphotoexcitation of the photocatalyst may be readily carried out even bythe sunlight as a light source.

[0109] Furthermore, in the event that the coating film is formed on aplastically deformable substrate such as a steel sheet, it is possibleto readily subject the steel sheet to plastic working as desired aftercuring of the coating film and prior to photoexcitation. Prior tophotoexcitation, the organic groups are bonded to the silicon atoms ofthe silicone molecules so that the coating film has an adequateflexibility. Accordingly, the steel sheet may be readily deformedwithout damaging the coating film. After plastic deformation, thephotocatalyst may be subjected to photoexcitation whereupon the organicgroups bonded to the silicon atoms of the silicone molecules will besubstituted with hydroxyl groups under the action of photocatalyst tothereby render the surface of the coating film superhydrophilic.

[0110] It is believed that the photocatalyst-containing silicone painthas a sufficient resistance to photooxidation action of thephotocatalyst because it is composed of the siloxane bond.

[0111] Another advantage of the photocatalytic coating made ofphotocatalyst-containing silicone paint is that, once the surface hasbeen rendered superhydrophilic, the superhydrophilicity is maintainedfor a long period of time even if the coating is kept in the dark and afurther advantage is that the superhydrophilicity can be restored evenby the light of an indoor illumination lamp such as fluorescent lamp.

[0112] Examples of the film forming element usable in the inventioninclude methyltrichlorosilane, methyltribromosilane,methyltrimethoxysilane, methyltriethoxysilane,methyltriisopropoxysilane, methyltri-t-buthoxysilane;ethyltrichlorosilane, ethyltribromosilane, ethyltrimethoxysilane,ethyltriethoxysilane, ethyltriisopropoxysilane,ethyltri-t-buthoxysilane; n-propyltrichlorosilane,n-propyltribromosilane, n-propyltrimethoxysilane,n-propyltriethoxysilane, n-propyltriisopropoxysilane,n-propyltri-t-buthoxysilane; n-hexyltrichlorosilane,n-hexyltribromosilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane,n-hexyltriisopropoxysilane, n-hexyltri-t-buthoxysilane;n-decyltrichlorosilane, n-decyltribromosilane, n-decyltrimethoxysilane,n-decyltriethoxysilane, n-decyltriisopropoxysilane,n-decyltri-t-buthoxysilane; n-octadecyltrichlorosilane,n-octadecyltribromosilane, n-octadecyltrimethoxysilane,n-octadecyltriethoxysilane, n-octadecyltriisopropoxysilane,n-octadecyltri-t-buthoxysilane; phenyltrichlorosilane,phenyltribromosilane, phenyltrimethoxysilane, phenyltriethoxysilane,phenyltriisopropoxysilane, phenyltri-t-buthoxysilane; tetrachlorosilane,tetrabromosilane, tetramethoxysilane, tetraethoxysilane,tetrabuthoxysilane, dimethoxydiethoxysilane; dimethyldichlorosilane,dimethyldibromosilane, dimethyldimethoxysilane, dimethyldiethoxysilane;diphenyldichlorosilane, diphenyldibromosilane, diphenyldimethoxysilane,diphenyldiethoxysilane; phenylmethyldichlorosilane,phenylmethyldibromosilane, phenylmethyldimethoxysilane,phenylmethyldiethoxysilane; trichlorohydrosilane, tribromohydrosilane,trimethoxyhydrosilane, triethoxyhydrosilane, triisopropoxyhydrosilane,tri-t-buthoxyhydrosilane; vinyltrichlorosilane, vinyltribromosilane,vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriisopropoxysilane,vinyltri-t-buthoxysilane; trifluoropropyltrichlorosilane,trifluoropropyltribromosilane, trifluoropropyltrimethoxysilane,trifluoropropyltriethoxysilane, trifluoropropyltriisopropoxysilane,trifluoropropyltrit-buthoxysilane;gamma-glycidoxypropylmethyldimethoxysilane,gamma-glycidoxypropylmethyldiethoxysilane,gamma-glycidoxypropyltrimethoxysilane,gamma-glycidoxypropyltriethoxysilane,gamma-glycidoxypropyltriisopropoxysilane,gamma-glycidoxypropyltri-t-buthoxysilane;gamma-methacryloxypropylmethyldimethoxysilane,gamma-methacryloxypropylmethyldiethoxysilane,gamma-methacryloxypropyltrimethoxysilane,gamma-methacryloxypropyltriethoxysilane,gamma-methacryloxypropyltriisopropoxysilane,gamma-methacryloxypropyltri-t-buthoxysilane;gamma-aminopropylmethyldimethoxysilane,gamma-aminopropylmethyldiethoxysilane,gamma-aminopropyltrimethoxysilane, gamma-aminopropyltriethoxysilane,gamma-aminopropyltriisopropoxysilane,gamma-aminopropyltri-t-buthoxysilane;gamma-mercaptopropylmethyldimethoxysilane,gamma-mercaptopropylmethyldiethoxysilane,gamma-mercaptopropyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane,gamma-mercaptopropyltriisopropoxysilane,gamma-mercaptopropyltri-t-buthoxysilane;β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltriethoxysilane; partial hydrolizates of anyof the foregoing; and mixtures of any of the foregoing.

[0113] To ensure that the silicone coating exhibits a satisfactoryhardness and smoothness, it is preferable that the coating contains (bymole percent) more than 10% of a three-dimensionally cross-linkingsiloxane. In addition, to provide an adequate flexibility of the coatingfilm yet assuring a satisfactory hardness and smoothness, it ispreferred that the coating contains less than 60% (by mole percent) of atwo-dimensionally cross-linking siloxane. Furthermore, to enhance thespeed that the organic groups bonded to the silicon atoms of thesilicone molecules are substituted with hydroxyl groups uponphotoexcitation, it is desirable to use a silicone wherein the organicgroups bonded to the silicon atoms of the silicone molecules aren-propyl or phenyl groups. In place of silicone having siloxane bonds,an organopolysilazane having silazane bonds may be used.

Addition of Antibacterial Enhancer

[0114] The photocatalytic coating may be doped with a metal such as Ag,Cu and Zn.

[0115] Doping of the photocatalyst with a metal such as Ag, Cu or Zn maybe carried out by adding a soluble salt of such metal to a suspensioncontaining particles of the photocatalyst, the resultant solution beingused to form the photocatalytic coating. Alternatively, after formingthe photocatalytic coating, a soluble salt of such metal may be appliedthereon and may be subjected to irradiation of light to deposit themetal by photoreduction.

[0116] The photocatalytic coating doped with a metal such as Ag, Cu orZn is capable of killing bacteria adhered to the surface. Moreover, suchphotocatalytic coating inhibits growth of microorganisms such as mold,algae and moss. As a result, the surface of a building, machine,apparatus, household, article and the like can be maintained clean for along period.

Addition of Photoactivity Enhancer

[0117] The photocatalytic coating may additionally be doped with a metalof the platinum group such as Pt, Pd, Rh, Ru, Os or Ir. These metals maybe similarly doped into the photocatalyst by photoreduction depositionor by addition of a soluble salt.

[0118] A photocatalyst doped with a metal of the platinum group developsan enhanced photocatalytic redox activity so that decomposition ofcontaminants adhering on the surface will be promoted.

Photoexcitation and UV Irradiation

[0119] For antifogging purposes (e.g., with respect to a transparentmember such as glass, a lens or a mirror), it is preferable that thephotocatalytic coating be formed from a photocatalyst such as titaniathat has a high band gap energy and can be photoexcited only by UVlight. In such event, the photocatalytic coating does not absorb visiblelight so that glass, a lens or a mirror, or other such transparentmember, would not be colored by a complementary color component. Theanatase form of titania may be photoexcited by a UV light having awavelength less than 387 nm, with the rutile form of titania by a UVlight having a wavelength less than 413 nm, with tin oxide by a UV lighthaving a wavelength less than 344 nm, with zinc oxide by a UV lighthaving a wavelength less than 387 nm.

[0120] As a source of UV light, a fluorescent lamp, incandescent lamp,metal halide lamp, mercury lamp or other type of indoor illuminationlamp may be used. As the antifogging glass, lens or mirror, or othertransparent member, is exposed to UV light, the surface thereof will besuperhydrophilified by photoexcitation of the photocatalyst. In asituation where the photocatalytic coating is exposed to sunlight as inthe case of a rearview mirror of a vehicle, the photocatalyst willadvantageously be photoexcited spontaneously by the UV light containedin the sunlight.

[0121] Photoexcitation may be carried out, or caused to be carried out,until the contact angle, with water, of the surface becomes less thanabout 10°, preferably less than about 5°, particularly equal to about0°. Generally, by photoexciting at a UV intensity of 0.001 mW/cm², thephotocatalytic coating will be superhydrophilified within several daysto the degree that the contact angle with water becomes about 0°. Sincethe intensity of the UV light contained in the sunlight impinging uponthe earth's surface is about 0.1-1 mW/cm², the surface will besuperhydrophilified in a shorter time when exposed to the sunlight.

[0122] In the case that the surface of the substrate is to beself-cleaned by rainfall or to be prevented from adhesion ofcontaminants, the photocatalytic coating may be formed of aphotocatalyst which can be photoexcited by UV light or visible light. Ifthe articles covered by the photocatalytic coating are disposedoutdoors, they will ordinarily be subjected to irradiation of thesunlight and to rainfall.

[0123] When the photocatalytic coating is made of titania-containingsilicone, it is preferable to photoexcite the photocatalyst at such anintensity to ensure that a sufficient amount of the surface organicgroups bonded to the silicon atoms of the silicone molecules aresubstituted with hydroxyl groups. The most convenient method therefor isto use the sunlight.

[0124] Once the surface has been made highly hydrophilic, thehydrophilicity is sustained even during the night. Upon exposure againto the sunlight, the hydrophilicity will be restored and maintained.

[0125] It is preferable that the photocatalytic coating issuperhydrophilified in advance before the substrate coated by thephotocatalytic coating according to the invention is offered for use tothe user.

EXAMPLES

[0126] The following Examples illustrate the industrial applicability ofthe invention from various aspects.

Example 1 Antifogging Mirror—Antifogging Photocatalytic Coating withInterleaved Silica Layer

[0127] 6 parts by weight of tetraethoxysilane Si(OC₂H₅)₄ (Wako JunYaku,Osaka), 6 parts by weight of pure water, and 2 parts by weight of 36%hydrochloric acid as a hydrolysis inhibitor were added to 86 parts byweight of ethanol as a solvent and the mixture was stirred to obtain asilica coating solution. The solution was allowed to cool for about 1hour since the solution evolved heat upon mixing. The solution was thenapplied on the surface of a soda-lime glass plate of 10 cm square insize by the flow coating method and was dried at a temperature of 80° C.As drying proceeds, tetraethoxysilane was hydrolyzed to first formsilanol Si(OH)₄ which then underwent dehydration polymerization to forma thin film of amorphous silica on the surface of the glass plate.

[0128] Then a titania coating solution was prepared by adding 0.1 partsby weight of 36% hydrochloric acid as a hydrolysis inhibitor to amixture of 1 part by weight of tetraethoxytitanium (Ti(OC₂H₅)₄)(Merck)and 9 parts by weight of ethanol, and the solution was applied to thesurface of the above-mentioned glass plate by the flow coating method indry air. The amount of coating was 45 μg/cm² in terms of titania. As thespeed of hydrolysis of tetraethoxytitanium was so high, hydrolysis oftetraethoxytitanium partially commenced during the course of coating sothat formation of titanium hydroxide Ti(OH)₄ started.

[0129] Then the glass plate was held at a temperature of about 150° C.for 1-10 minutes to permit completion of the hydrolysis oftetraethoxy-titanium and to subject the resultant titanium hydroxide todehydration polymerization whereby amorphous titania was formed. In thismanner, a glass plate was obtained having a coating of amorphous titaniaoverlying the coating of amorphous silica.

[0130] This specimen was then fired or calcined at a temperature of 500°C. in order to transform amorphous titania into the anatase form oftitania. It is considered that, due to the presence of the coating ofamorphous silica underlying the coating of amorphous titania, alkalinenetwork-modifier ions (such as sodium ions present in the glass plate)were prevented from diffusing from the glass substrate into the titaniacoating during calcination.

[0131] Then a reflective coating of aluminum was formed by vacuumevaporation deposition on the back of the glass plate to prepare amirror to thereby obtain #1 specimen.

[0132] After the #1 specimen was kept in the dark for several days, a UVlight was irradiated on the surface of the specimen for about one hourat a UV intensity of 0.5 mW/cm² (the intensity of UV light having anenergy higher than the band gap energy of the anatase form of titania,i.e., the intensity of UV light having a wavelength shorter than 387 nm)by using a 20 W blue-light-black (BLB) fluorescent lamp (SankyoElectric, FL20BLB) to obtain #2 specimen.

[0133] For the purposes of comparison, a reflective coating of aluminumwas formed by vacuum evaporation deposition on the back of a glass plateprovided neither with silica nor titania coating, the product beingplaced in the dark for several days to obtain #3 specimen.

[0134] The contact angle, with water, of the #2 and #3 specimens wasmeasured by a contact angle meter (Kyowa Kaimen Kagaku K.K. of Asaka,Saitama, Model CA-X150). The resolving power at the small angle side ofthis contact angle meter was 1°. The contact angle was measured 30seconds after a water droplet was dripped from a micro-syringe onto thesurface of the respective specimens. In the #2 specimen, the reading ofthe contact angle meter was 0° so that the surface exhibitedsuperhydrophilicity. In contrast, the contact angle with water of the #3specimen was 30-40°.

[0135] Then the #2 and #3 specimens were tested for antifoggingcapability, as well as to see how adherent water droplets would spreadover the surface. Assessment of the antifogging capability was done byfilling a 500 ml beaker with 300 ml of hot water at about 80° C., andthereafter placing each specimen on the beaker for about 10 seconds withthe front surface of the mirror directed downwards, and then inspectingimmediately thereafter the presence or absence of a fog on the surfaceof the specimen and inspecting how the face of the tester reflected.

[0136] With the #3 specimen, the surface of the mirror was fogged bysteam so that the image of the observer's face was not reflected well.However, with the #2 specimen, no fogging was observed at all and theface of the tester was clearly reflected.

[0137] Assessment of the spreading of adherent water droplets wascarried out by dripping several water droplets from a pipette onto themirror surface of each specimen inclined at an angle of 45°, rotatingthe mirror into a vertical position, and thereafter inspecting how thedroplets adhered and how the face of the observer reflected.

[0138] With the #3 specimen, dispersed discrete water droplets whichwere obstructive to the eye adhered on the mirror surface. As a result,the reflected image was disturbed by the refraction of light due toadherent droplets so that it was difficult to observe the reflectedimage with clarity. In contrast, with the #2 specimen, water dropletsadhered onto the mirror surface were allowed to spread over the surfaceto form a relatively uniform water film without forming discrete waterdroplets. Although a slight distortion of the reflected image due to thepresence of the water film was observed, it was possible to recognizethe reflected image of the tester's face with a sufficient clarity.

Example 2 Antifogging Mirror—Photocatalytic Coating ComprisingSilica-blended Titania

[0139] A thin film of amorphous silica was formed on the surface of amirror (made by Nihon Flat Glass, MFL3) in a manner similar to Example1.

[0140] Then a coating solution was prepared by admixing 0.69 g oftetraethoxysilane (Wako JunYaku), 1.07 g of a sol of the anatase form oftitania (Nissan Chemical Ind., TA-15, mean particle size of 0.01 μm),29.88 g of ethanol, and 0.36 g of pure water. The coating solution wasapplied on the surface of the mirror by spray coating process. Themirror was held at a temperature of about 150° C. for about 20 minutesto subject tetraethoxysilane to hydrolysis and dehydrationpolymerization to thereby form on the mirror surface a coating whereinparticles of the anatase form of titania were bound by a binder ofamorphous silica. The ratio by weight of titania to silica was 1.

[0141] After the mirror was kept in the dark for several days, a UVlight was irradiated by the BLB fluorescent lamp for about one hour, ata UV intensity of 0.5 mW/cm² to obtain #1 specimen. The contact anglewith water at the surface of the mirror was measured by the same contactangle meter as used in Example 1 and the reading of the contact anglemeter was 0°.

[0142] Then, in the manner similar to Example 1, the antifoggingcapability and the spreading of adherent water droplets were assessedwith respect to the coated #1 specimen, as well as to an “MFL3” mirrorspecimen not provided with a photocatalytic coating. In the test forantifogging property, with the coated #1 specimen, no fog was observedat all and the tester's face was clearly reflected, in contrast to theuncoated “MFL3” mirror wherein a fog was observed on the surface of themirror so that the image of the tester's face was not clearly reflected.In the inspection for spreading of adherent water droplets, with theuncoated “MFL3” mirror, water droplets remained as droplets on thesurface, causing refraction of light and thereby disturbing thereflected image, so that it was difficult to clearly observe thereflected image. With the coated #1 specimen, in contrast, waterdroplets on the mirror were spread over the surface to form a relativelyuniform water film and, although a slight distortion was observed in thereflected image due to the presence of the water film, it was possibleto recognize the reflected image of the tester's face with sufficientclarity.

Example 3 Antifogging Eyeglass Lens

[0143] First, a thin film of amorphous silica was formed in a mannersimilar to Example 1 on both sides of an eyeglass lens commerciallyavailable on the market.

[0144] Then, the coating solution similar to that of Example 2 was spraycoated on both sides of the lens and the lens was held at a temperatureof about 150° C. for about 20 minutes to subject tetraethoxysilane tohydrolysis and dehydration polymerization to thereby form on each sideof the lens a coating wherein particles of the anatase form of titaniawere bound by a binder of amorphous silica.

[0145] After the lens was kept in the dark for several days, it wasirradiated with UV light from a BLB fluorescent lamp for about one hourat a UV intensity of 0.5 mW/cm². When the contact angle with water atthe surface of the lens was measured by the same contact angle meter asused in Example 1, the reading of the contact angle meter was 0°. Thislens was mounted to the right-hand side of a pair of eyeglasses, with anordinary lens being mounted for the purposes of comparison to theleft-hand side.

[0146] When, several hours later, the tester wore the glasses and took abath for about 5 minutes, the ordinary lens on the left was fogged withsteam so that the eyesight was lost. However, formation of fog was notobserved at all on the right-hand lens coated with the photocatalyticcoating that had been subjected to UV irradiation.

[0147] As the tester then intentionally directed a shower on theglasses, obstructive water droplets adhered on the left-hand ordinarylens so that a view was interrupted. However, water droplets on theright-hand lens promptly spread into a water film so that a sufficientview, with adequate clarity, was secured.

Example 4 Antifogging Glass—7 nm Thick Titania Coating

[0148] A solution containing a chelate of titanium was applied to thesurface of a soda-lime glass plate (10 cm square in size) and thetitanium chelate was subjected to hydrolysis and dehydrationpolymerization to form amorphous titania on the surface of the glassplate. The plate was then calcined at a temperature of 500° C. to form asurface layer of crystals of the anatase form of titania. The thicknessof the surface layer was 7 nm.

[0149] The surface of the thus obtained specimen was first subjected toirradiation with UV light for about one hour, at a UV intensity of 0.5mW/cm², by using a BLB fluorescent lamp. The contact angle with water ofthe surface of this specimen was measured by a contact angle meter (madeby ERMA, Model G-I-1000, the resolving power at the small angle sidebeing 3° ), and the reading of the contact angle meter was less than 3.

[0150] Then, while irradiating with UV light at a UV intensity of 0.01mW/cm² by using a 20 W white fluorescent lamp (Toshiba, FL20SW), thevariation, in response to time, of the contact angle was measured. Theresults are plotted in the graph of FIG. 3. It will be noted from thegraph that the surface of the specimen was maintained highly hydrophiliceven by a weak UV light emitted from the white fluorescent lamp.

[0151] This Example illustrates that the surface of the photocatalytictitania coating can be maintained highly hydrophilic even though thethickness thereof is made as extremely small as 7 nm. This is veryimportant in preserving the transparency of a substrate such as awindowpane.

Example 5 Antifogging Glass—20 nm Thick Titania Coating

[0152] A surface layer of anatase-form titania crystals was formed onthe surface of a soda-lime glass plate in a manner similar to Example 4.The thickness of the surface layer was 20 nm.

[0153] Similar to Example 4, the surface of the thus obtained specimenwas first subjected to irradiation with UV light for about one hour, ata UV intensity of 0.5 mW/cm², by using a BLB fluorescent lamp. Then, thevariation in response to time of the contact angle was measured whilesubjecting the specimen to irradiation with UV light at a UV intensityof 0.01 mW/cm², by using a white fluorescent lamp. The results are shownin the graph of FIG. 4. In this Example, too, the surface of thespecimen was maintained highly hydrophilic by a weak UV light emittedfrom a white fluorescent lamp.

Example 6 Antifogging Glass—Effect of Calcination Temperature ofAmorphous Titania

[0154] In a manner similar to Example 1, a thin film of amorphous silicawas first formed on the surface of soda-lime glass plates (each 10 cmsquare in size) and then a thin film of amorphous titania was coatedthereon to obtain a plurality of specimens.

[0155] These glass plates were then calcined at temperatures of 450° C.,475° C., 500° C., and 525° C., respectively. Upon inspection by thepowder X-ray diffraction method, the presence of crystalline titania ofthe anatase form was detected in the specimens calcined at 475° C., 500°C., and 525° C. so that transformation of amorphous titania into theanatase form crystalline titania was confirmed in these specimens.However, in the specimen calcined at 450° C., the anatase form oftitania was not detected.

[0156] The surface of the thus obtained specimens was first subjected toirradiation with UV light for about three hours, at a UV intensity of0.5 mW/cm², by using a BLB fluorescent lamp. Then, the variation inresponse to time of the contact angle was measured by the contact anglemeter (CA-X150) while subjecting the specimen to irradiation with UVlight, at a UV intensity of 0.02 mW/cm², by using a white fluorescentlamp. The results are shown in Table 1. TABLE 1 Contact Angle (°)Calcination Immed. aft 3 days 9 days 14 days Temp (° C.) BLB irradnlater later later 450 10 13 15 23 475  0  0  0  0 500  0  0  0  0 525  0 0  0  0

[0157] As will be apparent from Table 1, it was found that, in thespecimens which were calcined at temperatures of 475° C., 500° C., and525° C., respectively, and in which the formation of anatase crystalswere confirmed, the contact angle was maintained at 0° and the surfaceof the glass plate was maintained superhydrophilic as long asirradiation with UV light by a white fluorescent lamp was continued. Incontrast, it was observed that the coating of amorphous titania of thespecimen calcined at 450° C. did not exhibit photocatalytic activity sothat the contact angle increased as time elapsed.

[0158] When a blow of breath was blown upon the specimens calcined attemperatures of 475° C., 500° C., and 525° C., respectively, noformation of fog was observed on the specimen surfaces.

Example 7 Antifogging Glass—Effect of Alkaline Network Modifier IonDiffusion

[0159] A titania coating solution similar to Example 1 was prepared andwas applied by the flow coating method on the surface of a soda-limeglass plate (10 cm square in size). Similar to Example 1, the amount ofcoating was 45 μg/cm² in terms of titania.

[0160] The glass plate was similarly held at a temperature of about 150°C. for 1-10 minutes to form amorphous titania on the surface of theglass plate. The specimen was then calcined at a temperature of 500° C.to transform amorphous titania into the anatase form of titania.

[0161] After keeping the specimen in the dark for several days, UV lightwas irradiated on the surface of the specimen for about one hour, at aUV intensity of 0.5 mW/cm², by using a BLB fluorescent lamp. Thereafter,the contact angle with water was measured by the contact angle meter(CA-X150), which indicated a contact angle of 3°.

[0162] It is considered that the reason why the contact angle for thisspecimen was not reduced to 0° is that because, contrary to Example 1,the specimen of this Example was not provided with a silica layerinterleaved between the glass substrate and the titania layer. Thus, thealkaline network-modifier ions (such as sodium ions) were allowed todiffuse from the glass substrate into the titania coating duringcalcination at 500° C., whereby the photocatalytic activity of titaniawas hindered.

[0163] It is therefore believed that, in order to realize thesuperhydrophilicity of such a degree that the contact angle with wateris equal to 0°, it is preferable to provide an intermediate layer ofsilica as in Example 1.

Example 8 Antifogging Glass—Formation of Amorphous Titania by Sputtering

[0164] A film of metallic titanium was deposited by sputtering on thesurface of a soda-lime glass plate (10 cm square in size). The glassplate was then calcined at a temperature of 500° C. Upon inspection bythe powder X-ray diffraction method, formation of the anatase form oftitania was observed on the surface of the glass plate. Metallictitanium was apparently oxidized into the anatase form by calcination.

[0165] Soon after calcination, the surface of the specimen was subjectedto irradiation with UV light, at a UV intensity of 0.5 mW/cm², by usinga BLB fluorescent lamp. The contact angle with water was then measuredby the contact angle meter (CA-X150) to monitor the variation inresponse to time of the contact angle, while irradiation continued. Theresults are shown in the graph of FIG. 5. As will be apparent from thegraph, the contact angle with water was kept less than 3°. Thisexperiment illustrates that, even in the case where the photocatalyticcoating is formed by sputtering, the surface of a glass plate ismaintained highly hydrophilic upon UV irradiation.

Example 9 Antifogging Glass—UV Intensity of 800 Lux

[0166] A thin film of amorphous silica was formed on the surface of a 10cm-square soda-lime glass plate in a manner similar to Example 1.

[0167] Then the coating solution of Example 2 was applied by spraycoating on the surface of the glass plate. The glass plate was then heldat a temperature of about 150° C. for about 20 minutes whereby a coatingin which particles of the anatase form of titania were bound by a binderof amorphous silica was formed on the surface of the glass plate. Theratio by weight of titania to silica was 1.

[0168] After being kept in the dark for several days, the glass platewas subjected to irradiation with UV light for about one hour, at a UVintensity of 0.5 mW/cm², by a BLB fluorescent lamp. After UVirradiation, the contact angle with water of the surface of the glassplate was measured by the contact angle meter (CA-X150) and it was foundthat the contact angle was 0°.

[0169] Thereafter, the specimen was subjected to irradiation with UVlight for 4 days, at a UV intensity of 0.004 mW/cm² (800 lux), by usinga white fluorescent lamp. While the specimen was under UV irradiation,the contact angle at the surface thereof was maintained less than 2°.When 4 days later a blow of breath was blown upon the specimen,formation of fog was not observed.

[0170] In this way, it was confirmed that, even with a weak UV lightsuch as is available for indoor illumination achieved, for example, by awhite fluorescent lamp, the surface of the glass plate was maintainedhighly hydrophilic and fogging of the glass plate was prevented.

Example 10 Antifogging Glass—Effect of Silica-to-Titania Blending Ratio

[0171] Next, tetraethoxysilane (Wako JunYaku), a sol of the anatase formof titania (Nissan Chemical Ind., TA-15), ethanol, and pure water wereadmixed in varying rate to prepare four kinds of coating solutionshaving different tetraethoxysilane-to-titania sol blending ratios. Theratios of tetraethoxysilane to titania sol were selected so that, aftertetraethoxysilane was converted into amorphous silica, the ratio ofsilica to the sum of silica plus titania was equal, by mole percent, to10%, 30%, 50%, and 70%, respectively.

[0172] Each of the coating solutions was applied by spray coating on thesurface of a 10 cm-square soda-lime glass plate which was then held at atemperature of about 150° C. for about 20 minutes to subjecttetraethoxysilane to hydrolysis and dehydration polymerization. Thus, acoating in which particles of the anatase form of titania were bound bya binder of amorphous silica was formed on the surface of the glassplate.

[0173] After being kept in the dark for a week, the specimens weresubjected to irradiation with UV light for about one hour, at a UVintensity of 0.3 mW/cm², by a BLB fluorescent lamp. After UVirradiation, the contact angle with water was measured for the surfaceof the respective specimens using the contact angle meter (CA-X150). Thecontact angle was 0° throughout all the specimens.

[0174] Thereafter, two specimens with coatings having 30% by mol and 50%by mol of silica, respectively, were subjected to irradiation with UVlight for 3 days, at a UV intensity of 0.004 mW/cm², by using a whitefluorescent lamp. While the specimens were under irradiation, thecontact angle at the surface thereof was maintained less than 3°.

Example 11 Antifogging Glass—Rutile Form Photocatalytic Coating

[0175] A titania coating solution was prepared by adding 0.1 part byweight of 36% hydrochloric acid as a hydrolysis inhibitor to a mixtureof 1 part by weight of tetraethoxytitanium (Ti(OC₂H₅)₄) (Merck) and 9parts by weight of ethanol. The solution was then applied to the surfaceof a plurality of quartz glass plates (10 cm square in size) by the flowcoating method in dry air. The amount of coating was 45 μg/cm² in termsof titania.

[0176] The glass plates were then held at a temperature of about 150° C.for 1-10 minutes to subject tetraethoxytitanium to hydrolysis anddehydration polymerization whereby a coating of amorphous titania wasformed on the surface of each glass plate.

[0177] These specimens were then calcined at temperatures of 650° C. and800° C., respectively, to subject amorphous titania to crystallization.Upon inspection by the powder X-ray diffraction method, it was foundthat the crystal form of the specimen calcined at 650° C. was of theanatase form while the crystal form of the specimen calcined at 800° C.was of the rutile form.

[0178] After keeping the thus obtained specimens in the dark for a week,they were subjected to irradiation with UV light for 2 days, at a UVintensity of 0.3 mW/cm², by a BLB fluorescent lamp. After UVirradiation, the contact angle was measured. The contact angle withwater of the surface was 0 throughout all the specimens.

[0179] It will be understood from the foregoing that a surface can bemaintained highly hydrophilic not only in the case that thephotocatalyst is the anatase form of titania but also in the case thatthe photocatalyst is the rutile form.

[0180] For this reason, it seems that the phenomenon of photocatalyticsuperhydrophilification is not altogether the same as the photocatalyticredox reaction.

Example 12 Antifogging Glass—Transmittance Test

[0181] In a manner similar to Example 1, a thin film of amorphous silicawas first formed on the surface of a soda-lime glass plate (10 cm squarein size) and then a thin film of amorphous titania was coated thereon.The glass plate was then calcined at a temperature of 50020 C. totransform amorphous titania into the anatase form of titania. Thespecimen thus obtained was kept in the dark for several days. Then thespecimen was placed in a desiccator (24° C. in temperature and 45-50% inhumidity) housing a BLB fluorescent lamp and was subjected toirradiation with UV light for one day, at a UV intensity of 0.5 mW/cm²,to obtain #1 specimen. The contact angle with water of the #1 specimenas measured was 0 .

[0182] Then the #1 specimen was taken out of the desiccator and waspromptly positioned above a warm bath held at 60° C. and transmittancewas measured 15 seconds later. The transmittance as measured was dividedby the initial transmittance to calculate a change in transmittancecaused by any fog formed through condensation of steam.

[0183] In a manner similar to Example 7, the surface of a glass platewas coated by the anatase form of titania to obtain #2 specimen. The #2specimen was placed in the desiccator and was subjected to irradiationwith UV light, at a UV intensity of 0.5 mW/cm², until the contact anglewith water became equal to 3°.

[0184] The #2 specimen was then placed in a dark place. The #2 specimenwas taken out of the dark place at different time points and each timethe contact angle with water was measured. In addition, at each point,the #2 specimen was placed in the desiccator (24° C. in temperature and45-50% in humidity) until the temperature was equalized whereupon, in amanner similar to the #1 specimen, the #2 specimen was promptly placedabove a warm bath held at 6020 C. and the transmittance was measured 15seconds later to derive a change in transmittance caused by a fog formedby condensation of steam.

[0185] For purposes of comparison, the contact angle with water was alsomeasured with respect to commercially marketed flat glass, acrylic resinplate, polyvinylchloride (PCV) plate and polycarbonate (PC) plate,respectively. Thereafter, each of these materials was placed in adesiccator, held under the same condition, to equalize the temperatureand was then promptly placed above a warm bath held at 60° C., thetransmittance being similarly measured 15 seconds later whereby a changein transmittance caused by a fog formed by condensation of steam wascalculated.

[0186] The results are shown in Table 2. TABLE 2 Contact Angle withChange in Specimen Water (°) Transmittance (%) #1 0 100 #2 (3 hrs later)5.0 100 #2 (6 hrs later) 7.7 100 #2 (8 hrs later) 8.2 100 #2 (24 hrslater) 17.8 89.8 #2 (48 hrs later) 21.0 88.5 #2 (72 hrs later) 27.9 87.0Flat Glass 40.6 45.5 Acrylic Resin Plate 64.5 60.6 PVC Plate 75.3 44.7PC Plate 86.0 49.0

[0187] As will be apparent from Table above, it was confirmed that anextremely high antifogging capability could be achieved if the contactangle with water was not greater than 10°.

Example 13 Photocatalyst-containing Silicone Coating

[0188] This Example is related to the discovery that a coating of acertain high molecular weight compound and containing a photocatalyst isrendered highly hydrophilic when subjected to irradiation with UV light.

[0189] As substrates, aluminum plates (10 cm square in size) were used.Each of the substrates was first coated with a silicone layer to smooththe surface. To this end, a first component “A” (silica sol) and asecond component “B” (trimethoxymethylsilane) of the coating composition“Glaska” marketed by Japan Synthetic Rubber Co. (Tokyo) were mixed witheach other in such a manner that the ratio by weight of silica totrimethoxymethylsilane was equal to 3. The resultant coating mixture wasapplied on each of the aluminum substrates and was subjected to curingat a temperature of 150° C. to obtain a plurality of aluminum substrates(#1 specimens) each coated with a base coating of silicone of 3 μm inthickness.

[0190] Then, the #1 specimens were coated with a high-molecular-weightcoating composition containing a photocatalyst. In order to prevent afilm forming element of the coating composition from being degraded byphotooxidation action of the photocatalyst, silicone was selected as thefilm forming element.

[0191] More specifically, a sol of the anatase form of titania (NissanChemical Ind., TA-15) and the first component “A” (silica sol) of theabove-mentioned “Glaska” were admixed. After dilution by ethanol, theabove-mentioned second component “B” of “Glaska” was further addedthereto to prepare a titania containing coating composition. The coatingcomposition was comprised of 3 parts by weight of silica, 1 part byweight of trimethoxymethylsilane, and 4 parts by weight of titania.

[0192] The coating composition was applied onto the surface of the #1specimens and was cured at a temperature of 150° C. to obtain #2specimens coated with a top coating wherein particles of the anataseform of titania were dispersed throughout a coating film of silicone.

[0193] Then the #2 specimens were subjected to irradiation with UV lightfor 5 days, at a UV intensity of 0.5 mW/cm², by using a BLB fluorescentlamp to obtain #3 specimens. When the contact angle with water of thesurface of these specimens was measured by the contact angle meter (madeby ERMA), surprisingly the reading of the contact angle meter was lessthan 3°.

[0194] The contact angle of the #2 specimens measured prior to UVirradiation was 70°. The contact angle of the #1 specimens as measuredwas 90°. Then, the #1 specimens were subjected further to irradiationwith UV light for 5 days under the same condition as the #2 specimensand the contact angle thereof was measured, the contact angle asmeasured being 85°.

[0195] From the foregoing, it has been discovered that, notwithstandingthe fact that silicone inherently is substantially hydrophobic, siliconeis rendered highly hydrophilic when it contains a photocatalyst andprovided that the photocatalyst is photoexcited by irradiation with UVlight.

Example 14 Raman Spectroscopic Analysis

[0196] By using a mercury lamp, the #2 specimen of Example 13 wassubjected to irradiation with UV light for 2 hours, at a UV intensity of22.8 mW/cm², to obtain #4 specimen. The #2 specimen prior to UVirradiation and the #4 specimen subsequent to UV irradiation weresubjected to Raman spectroscopic analysis. For the purposes ofcomparison, a UV light was irradiated upon the #1 specimen under thesame conditions and the specimen was subjected to Raman spectroscopicanalysis prior to and subsequent to UV irradiation. Raman spectra areshown in the graph of FIG. 6. In the graph of FIG. 6, the Raman spectraof the #1 specimen prior to and subsequent to UV irradiation are shownby the single curve #1 because they are identical.

[0197] Referring to the graph of FIG. 6, in the Raman spectrum of the #2specimen, a dominant peak is noted at the wavenumber 2910 cm⁻¹corresponding to the symmetrical stretching of the C—H bond of the sp³hybrid orbital and a salient peak is observed at the wavenumber 2970cm⁻¹ indicating the inverted symmetrical stretching of the C—H bond ofthe sp³ hybrid orbital. It can therefore be concluded that the C—H bondsare present in the #2 specimen.

[0198] In the Raman spectrum of the #4 specimen, no peak is found at thewavenumbers 2910 cm⁻¹ and 2970 cm⁻¹. Instead, a broad absorption bandpeaking at the wavenumber 3200 cm⁻¹ and corresponding to the symmetricalstretching of the O—H bond is observed. It is therefore concluded that,in the #4 specimen, there is no C—H bond but, instead, the O—H bonds arepresent.

[0199] In contrast, in the Raman spectrum of the #1 specimen, a dominantpeak at the wavenumber 2910 cm⁻¹ corresponding to the symmetricalstretching of the C—H bond of the sp³ hybrid orbital as well as asalient peak at the wavenumber 2970 cm⁻¹ corresponding to the invertedsymmetrical stretching of the C—H bond of the sp³ hybrid orbital arenoted throughout the points of time prior to and subsequent to UVirradiation. Accordingly, it is confirmed that the C—H bonds are presentin the #1 specimen.

[0200] From the foregoing, it is considered that, when silicone whichcontains a photocatalyst is subjected to irradiation with UV light, theorganic groups bonded to the silicon atoms of the silicone molecules asrepresented by the general formula (1) below are substituted with thehydroxyl groups under the action of the photocatalyst so that aderivative of silicone is formed at the surface as shown by the formula(2).

[0201] where R represents alkyl or aryl group.

Example 15 Antifogging Plastic Plate—Antifogging Coating ofPhotocatalyst-containing silicone

[0202] The surface of a plastic substrate was first coated with asilicone layer to prevent the substrate from being degraded by thephotocatalyst.

[0203] To this end, a coating solution was prepared in a manner similarto Example 13 by admixing the first and second components “A” and “B” ofthe above-mentioned “Glaska” of Japan Synthetic Rubber Co. such that theratio by weight of silica to trimethoxymethylsilane was equal to 3. Thecoating solution was applied on the surface of 10 cm-square acrylicresin plates, and each plate was then cured at a temperature of 100° C.to obtain a plurality of acrylic resin plates (#1 specimens) each coatedwith a base coating of silicone of 5 μm in thickness.

[0204] Next, a sol of the anatase form of titania (Nissan Chemical Ind.,TA-15) and the first component “A” of the above-mentioned “Glaska” wereadmixed and, after diluted by ethanol, the second component “B” of“Glaska” was added thereto to prepare four kinds of coating solutionshaving different compositions. The compositions of these coatingsolutions were such that the ratio by weight of titania to the sum oftitania plus silica plus trimethoxymethylsilane was equal to 5%, 10%,50%, and 80%, respectively.

[0205] These coating solutions were applied, respectively, onto thesurface of the acrylic resin plates coated with the silicone layer andwere cured at a temperature of 100° C. to obtain #2-#5 specimens eachcoated with a top coating wherein particles of the anatase form oftitania were dispersed throughout a coating film of silicone.

[0206] Then the #1-#5 specimens were subjected to irradiation with UVlight by a BLB fluorescent lamp for maximum 200 hours, at a UV intensityof 0.5 mW/cm², and the contact angle with water of the surface of thesespecimens was measured by the contact angle meter (made by ERMA) atdifferent time points to see the variation in response to time of thecontact angle. The results are shown in the graph of FIG. 7.

[0207] As will be understood from the graph of FIG. 7, in the #1specimen, which was not provided with A titania-containing coating, noappreciable change in the contact angle with water resulted from UVirradiation.

[0208] In contrast, in each of the #2-#5 specimens (each of which had atitania-containing top coating), it will be noted that upon UVirradiation the surface was rendered hydrophilic to the degree that thecontact angle with water became less than 10°.

[0209] In particular, it will be understood that, in the #3-#5 specimenswherein the titania content was greater than 10% by weight, the contactangle with water became less than 3°.

[0210] Furthermore, it will be noted that in the #4 and #5 specimenshaving a titania contents of 50% by weight and 80% by weight,respectively, the contact angle with water became less than 3° within arelatively short time of beginning UV irradiation.

[0211] When a blow of breath was blown upon the #4 specimen, noformation of fog was observed. After keeping the #4 specimen in the darkfor 2 weeks, the contact angle with water was measured by the contactangle meter (CA-X150) and was found to be less than 3°.

Example 16 Pencil Scratch Test

[0212] A pencil scratch test was conducted to ascertain the abrasionresistance of the titania-containing top coating.

[0213] In a manner similar to Example 15, a plurality of 10 cm-squareacrylic resin plates were first coated with a base coating of siliconeof 5 μm in thickness and were then coated with a top coating havingvarying titania content. In these plates, the titania content of the topcoating was 50% by weight, 60% by weight, and 90% by weight,respectively.

[0214] According to the method H8602 of the Japanese Industrial Standard(JIS), the surface of the specimens was scratched by various pencilleads to find the hardest pencil lead by which the top coating waspeeled off. A similar test was also conducted for a specimen which wascoated only with the base coating. The results are shown in the graph ofFIG. 8.

[0215] The top coating having a titania content of 90% by weight waspeeled off by a pencil lead of hardness 5B, but the top coating having atitania content of 60% by weight was able to withstand a pencil lead ofhardness H and showed an adequate abrasion resistance. The abrasionresistance of the top coating apparently increases with decreasingtitania content.

Example 17 Effect of Coating Thickness

[0216] In a manner similar to Example 13, a plurality of 10 cm-squarealuminum plates were first coated with a base coating of silicone of 5μm in thickness and were then coated with an anatase-containing topcoating of varying thickness to obtain a plurality of specimens. Thethickness of the top coating of the #1 specimen was 0.003 μm, thethickness of the top coating of the #2 specimen being 0.1 μm, thethickness of the top coating of the #3 specimen being 0.2 μm, thethickness of the top coating of the #4 specimen being 0.6 μm, and thethickness of the top coating of the #5 specimen being 2.5 μm.

[0217] While subjecting the respective specimens to irradiation with UVlight, at a UV intensity of 0.5 mW/cm² by using a BLB fluorescent lamp,the variation in response to time of the contact angle with water of thesurface of the specimens was measured by the contact angle meter (madeby ERMA). The results are shown in the graph of FIG. 9.

[0218] As will be apparent from the graph of FIG. 9, regardless of thethickness of the coating, the surface of the respective specimens wasrendered highly hydrophilic within 50 hours of UV irradiation to thedegree that the contact angle with water became less than 3°. It will benoted in particular that, even with the titania-containing top coatingof the thickness of less than 0.2 μm, a sufficient photocatalyticactivity was achieved to the degree that the top coating surface wasrendered highly hydrophilic. In this regard, it is known that atransparent layer is colored due to interference of light when thethickness of the layer exceeds 0.2 μm. This Example illustrates that, bylimiting the thickness of the top coating to 0.2 μm or less, the surfaceof the top coating can be made highly hydrophilic while preventingcoloring thereof due to interference of light.

[0219] Next, the #1-#5 specimens were tested for the capability thereofto photodecompose methyl mercaptan. Each specimen was placed,separately, in a desiccator of 11 liters in volume made of UV permeablequartz glass, and nitrogen gas containing methyl mercaptan wasintroduced therein in such a manner that the methyl mercaptanconcentration equaled 3 ppm. A 4 W BLB fluorescent lamp was placedwithin the desiccator at a distance of 8 cm from the specimen toirradiate the specimen, at a UV intensity of 0.3 mW/cm². By sampling gasin the desiccator 30 minutes later, the methyl mercaptan concentrationwas measured by gas chromatography and the removal rate of methylmercaptan was calculated. The results are shown in the graph of FIG. 10.

[0220] The graph of FIG. 10 indicates that the photodecompositioncapability of the photocatalytic coating vis-a-vis methyl mercaptanincreases with increasing coating thickness. It is found that thephotocatalytic photodecomposition capability was clearly affected by thethickness of the photocatalytic layer. In view of the results shown inFIG. 9, it seems that the photocatalytic superhydrophilification processis not necessarily identical with the photocatalytic redox process knownhitherto in the field of photocatalyst.

Example 18 Highly Hydrophilic Photocatalytic Coating ofTitania-containing Silicone

[0221] In a manner similar to Example 13, a 10 cm-square aluminum platewas first coated with a base coating of silicone of 5 μm in thickness.

[0222] Then, a sol of the anatase form of titania (Nissan Chemical Ind.,TA-15) and the second component “B” (trimethoxymethylsilane) of theabove-mentioned “Glaska” were admixed with each other and the mixturewas diluted by ethanol to prepare a coating composition containingtitania. The ratio by weight of trimethoxymethylsilane to titania wasequal to 1.

[0223] The coating composition was applied onto the surface of thealuminum plate and was cured at a temperature of 150° C. to form a topcoating wherein particles of the anatase form of titania were dispersedthroughout a coating film of silicone. The thickness of the coating was0.1 μm.

[0224] Then the specimen was subjected to irradiation with UV light fora day, at a UV intensity of 0.5 mW/cm², by using a BLB fluorescent lamp.When the contact angle with water of the surface of this specimen wasmeasured by the contact angle meter (CA-X150), the reading of contactangle was 0°.

[0225] The specimen was kept in the dark for 3 weeks and the contactangle with water was measured each week. The measured contact angle isshown in Table 3. TABLE 3 immed. after irradation 1 week later 2 weekslater 3 weeks later 0° 2° 1° 3°

[0226] As will be understood from Table 3, once the surface has beensuperhydrophilified, superhydrophilicity will be sustained for asubstantially long time period even in the absence of photoexcitation.

Example 19 Antibacterial Enhancer—Ag-added Photocatalyst

[0227] In a manner similar to Example 1, a thin film of amorphous silicaand a thin film of amorphous titania were formed in sequence on thesurface of a 10 cm-square soda-lime glass plate and the glass plate wasthen calcined at a temperature of 500° C. to transform amorphous titaniainto the anatase form of titania, whereby #1 specimen was obtained.

[0228] Then an aqueous solution containing 1% by weight of silverlactate was applied onto the surface of the #1 specimen, and thespecimen was subjected to irradiation with UV light for one minute byoperating a 20 W BLB fluorescent lamp positioned at a distance of 20 cmfrom the specimen whereby #2 specimen was obtained. Upon UV irradiation,silver lactate underwent photoreduction to form silver deposit and thesurface of the specimen was rendered hydrophilic under thephotocatalytic action of titania. The #1 specimen was also subjected toUV irradiation under the same conditions.

[0229] When the contact angle with water of the #1 and #2 specimens wasmeasured by the contact angle meter (made by ERMA), the contact angle inboth specimens was less than 3°. When a blow of breath was blown uponthese specimens, no formation of fog was observed. For the purposes ofcomparison a substrate of soda-lime glass, without coating, was tested,and it was found that the contact angle with water was 50° and a fog wasreadily formed upon blowing of breath.

[0230] Then, the #1 and #2 specimens as well as the uncoated soda-limeglass plate were tested for antibacterial capability. A liquid cultureprepared by shake cultivating colibacillus (Escherichia coli W3110stock) for a night was subjected to centrifugal washing and was dilutedwith sterilized distilled water by 10,000 times to prepare a bacteriacontaining liquid. 0.15 ml of the bacteria containing liquid (equivalentto 10000-50000 CFU) was dripped on three glass slides which were thenbrought into intimate contact with the #1 and #2 specimens and theuncoated soda-lime glass plate, respectively, all of which hadpreviously been sterilized by 70% ethanol. The specimens and theuncoated plate were then subjected to irradiation from a whitefluorescent lamp placed in front of the glass slides for 30 minutes, atan intensity of 3500 lux. Thereafter, the bacteria containing liquid ofrespective specimens was wiped by a sterilized gauze and was recoveredin 10 ml of physiological saline and the liquid thus recovered wasapplied for inoculation on a nutrient agar plate for culture at 37° C.for a day. Thereafter, the colonies of colibacillus formed on theculture was counted to calculate the survival rate of colibacillus. Theresult was that in the #1 specimen and the soda-lime glass plate thesurvival rate of colibacillus was greater than 70%, but the survivalrate was less than 10% in the #2 specimen.

[0231] This experiment demonstrates that, when the photocatalyst isdoped with Ag, the surface of the substrate is not only rendered highlyhydrophilic but also becomes antibacterial.

Example 20 Antibacterial Enhancer—Cu-added Photocatalyst

[0232] In a manner similar to Example 1, a thin film of amorphous silicawas formed on the surface of each of a plurality of 10 cm-squaresoda-lime glass plates to obtain a plurality of #1 specimens.

[0233] Then, similar to Example 1, a thin film of amorphous titania wasformed on the surface of one #1 specimen which was then calcined at atemperature of 500° C. to transform amorphous titania into the anataseform titania. Then an ethanol solution containing 1 weight percent ofcopper acetate was applied by spray coating onto the surface of onespecimen and, after drying, the specimen was subjected to irradiationwith UV light for one minute by a 20 W BLB fluorescent lamp positionedat a distance of 20 cm from the specimen, to thereby subject copperacetate to photoreduction deposition and, thus, to obtain a #2 specimenwherein crystals of titania were doped with copper. As inspected by theeye, the #2 specimen presented an adequate light transmittance.

[0234] A soda-lime glass plate as well as the #2 specimen and the #1specimen (without titania coating) immediately after fabrication weretested for antifogging capability and the contact angle with watermeasured. The antifogging test was done by blowing a blow of breath uponthe specimen to produce a fog on the specimen surface and by inspectingfor the presence or absence of particles of moisture condensate, using amicroscope. The contact angle was measured by the contact angle meter(made by ERMA). The results are shown in Table 4. TABLE 4 ImmediatelyAfter Preparation of Specimen Contact Angle with Antifogging Water (°)Property #2 Specimen 10 no fog #1 Specimen  9 no fog Soda-Lime Glass 50fogged

[0235] Further, after being subjected to irradiation with UV light for amonth, at a UV intensity of 0.5 mW/cm², by a BLB fluorescent lamp, the#2 and #1 specimens and the soda-lime glass plate were tested in asimilar manner for antifogging capability and contact angle. The resultsare shown in Table 5. TABLE 5 After 1 Month of UV Irradation ContactAngle with Antifogging Water (°) Property #2 Specimen  3 no fog #1Specimen 49 fogged Soda-Lime Glass 53 fogged

[0236] Then, the #2 and #1 specimens immediately after preparation andthe soda-lime glass plate were tested for antibacterial capability in amanner similar to that described in Example 19. The result was that inthe soda-lime glass plate and the #1 specimen the survival rate ofcolibacillus was greater than 70%, but the survival rate was less than10% in the #2 specimen.

[0237] Next, the #2 and #1 specimens immediately after preparation, andthe uncoated soda-lime glass plate, were tested for deodorizingperformance. Each specimen was placed in a desiccator of 11 liters involume made of UV permeable quartz glass and nitrogen gas containingmethyl mercaptan was introduced therein in such a manner that the methylmercaptan concentration equaled 3 ppm. In each case, a 4 W BLBfluorescent lamp was placed within the desiccator at a distance of 8 cmfrom the specimen to irradiate the specimen, at a UV intensity of 0.3mW/cm². By sampling gas in the desiccator 30 minutes later, the methylmercaptan concentration was measured by gas chromatography and theremoval rate of methyl mercaptan was calculated. With the #1 specimenand the soda-lime glass plate, the removal rate of methyl mercaptan wasless than 10%. In contrast, the removal rate of the #2 specimen was morethan 90%, so that a good deodorizing performance was achieved.

Example 21 Antibacterial Enhancer—Cu-added Photocatalyst

[0238] The first and second components “A” (silica sol) and “B”(trimethoxymethylsilane) of “Glaska” of Japan Synthetic Rubber Co. wereadmixed such that the ratio by weight of silica totrimethoxymethylsilane was equal to 3, and the mixture was applied onthe surface of a 10 cm-square acrylic resin plate, followed by curing ata temperature of 100° C. to obtain an acrylic resin plate coated with abase coating of silicone of 3 μm in thickness.

[0239] Then, a sol of the anatase form of titania (TA-15) and an aqueoussolution containing 3 weight percent of copper acetate were mixed and,after adding further the first component “A” (silica sol) of “Glaska”thereto, the mixture was diluted by propanol. Then the second component“B” of “Glaska” was further added to prepare a titania-containingcoating composition. The coating composition was comprised of 3 parts byweight of silica, 1 part by weight of trimethoxymethylsilane, 4 parts byweight of titania, and 0.08 parts by weight of copper acetate in termsof metallic copper.

[0240] The coating composition was applied onto the surface of theacrylic resin plate and was cured at a temperature of 100° C. to form atop coating. Then the specimen was subjected to irradiation with UVlight for 5 days, at a UV intensity of 0.5 mW/cm² by using a BLBfluorescent lamp to obtain #1 specimen.

[0241] The #1 specimen and the acrylic resin plate were investigated forantifogging capability, contact angle with water, antibacterialperformance and deodorizing function, in a manner similar to Example 20.In the acrylic resin plate, the contact angle with water was 70° and afog was formed as a blow of breath was blown upon. In the #1 specimen,however, the contact angle with water was 3-9° and formation of fog didnot occur. With regard to antibacterial property, in the acrylic resinplate the survival rate of colibacillus was greater than 70%, whereasthe survival rate was less than 10% in the #1 specimen. Regarding thedeodorizing property, while the removal rate of methyl mercaptan by theacrylic resin plate was less than 10%, the removal rate by the #1specimen was more than 90%.

Example 22 Photo-redox Activity Enhancer—Pt-added Photocatalyst

[0242] In a manner similar to Example 1, a thin film of amorphous silicaand then a thin film of amorphous titania were formed on the surface ofa 10 cm-square soda-lime glass plate and the glass plate was thencalcined at a temperature of 500° C. to transform amorphous titania intothe anatase form titania.

[0243] Then, 1 ml of aqueous solution of chloroplatinic acid 6-hydrateH₂PtCl₆.6H₂O containing 0.1 weight percent of platinum was applied ontothe specimen which was then subjected to irradiation with UV light forone minute, at a UV intensity of 0.5 mW/cm² by a BLB fluorescent lamp tothereby form deposit of platinum by photoreduction of chloroplatinicacid hexahydrate to obtain a specimen wherein crystals of titania weredoped with platinum.

[0244] The specimen thus obtained was left as such for a day and wasthereafter subjected to irradiation with UV light for a day, at a UVintensity of 0.5 mW/cm² by using a BLB fluorescent lamp. The contactangle measured after UV irradiation was 0°. Furthermore, the removalrate of methyl mercaptan as measured and calculated in a manner similarto Example 20 was 98%.

Example 23 Self-cleaning and Antifouling Capability

[0245] The #2 specimen of Example 13 was subjected to irradiation withUV light for 10 hours, at a UV intensity of 0.5 mW/cm² by using a BLBfluorescent lamp to obtain #3 specimen. When the contact angle withwater of the surface of this specimen was measured by the contact anglemeter (made by ERMA), the reading of the contact angle meter was lessthan 3°.

[0246] An outdoor accelerated fouling test apparatus as shown in FIGS.11A and 11B was installed atop of a building located in Chigasaki City.Referring to FIGS. 11A and 11B, this apparatus includes an inclinedspecimen mounting surface 22 supported by a frame 20 and adapted toaffix specimens 24 thereto. A forwardly slanted roof 26 is fixed at thetop of the frame. The roof is made of corrugated plastic sheet and isdesigned to permit collected rain water to flow down in a stripedpattern along the surface of the specimens 24 affixed on the specimenmounting surface 22.

[0247] The #3 specimens, the #1 specimens of Example 13, and the #2specimens of Example 13 were mounted to the specimen mounting surface 22of the apparatus and were exposed to the weather conditions for 9 daysstarting from Jun. 12, 1995. The weather and the amount of rain fallduring this period were as shown in Table 6. TABLE 6 Date WeatherRainfall (mm) Shining Hours June 12 cloudy 0.0 0 June 13 heavy rain 53.00 June 14 cloudy/rain 20.5 0 June 15 cloudy/fair 0.0 3.9 June 16 cloudy0.0 0.2 June 17 fair/cloudy 0.0 9.6 June 18 fair to cloudy 0.0 7.0 June19 rain to cloudy 1.0 0.2 June 20 cly/heavy rain 56.0 2.4

[0248] When inspected on June 14, dirt or smudge of a striped patternwas observed on the surface of the #1 specimen. Presumably, this isbecause during heavy rainfall on the preceding day the airbornehydrophobic contaminants such as combustion products like carbon blackand city grime were carried by rain and were allowed to deposit on thespecimen surface as rain water flowed down along the surface. Incontrast, no dirt or smudge was observed in the #3 specimen. Believably,this is because, since the specimen surface was rendered highlyhydrophilic, the hydrophobic contaminants were unable to adhere onto thesurface as rain water containing contaminants flowed down and furtherbecause the contaminants were washed away by rainfall.

[0249] In the #2 specimen, dirt or smudge of a mottled pattern wasobserved. This is probably because, after the #2 specimen which had notbeen subjected to UV irradiation was mounted to the testing apparatus,the photocatalytic coating thereof was not yet exposed to UV light inthe sunlight to a satisfactory degree so that the surface was unevenlyhydrophilified.

[0250] When inspected on June 20, a smudge of a vertically stripedpattern was remarkably noticed on the surface of the #1 specimen whichwas not provided with the photocatalytic coating. Conversely, no smudgewas observed on the #3 and #2 specimens provided with the photocatalyticcoating.

[0251] The contact angle with water as measured was 70° for the #1specimen and was less than 3° for the #2 and #3 specimens. The fact thatthe contact angle of the #2 specimen became less than 3° demonstratesthat, upon irradiation by UV light contained in the sunlight, theorganic groups bonded to the silicon atoms of the silicone molecules ofthe top coating were substituted with hydroxyl groups under thephotocatalytic action so that the top coating was rendered highlyhydrophilic. It was also noted that in the #3 specimen a high degree ofhydrophilicity was sustained by irradiation of the sunlight.

Example 24 Color Difference Test

[0252] Prior to and 1 month after mounting to the outdoor acceleratedfouling test apparatus, the #1 and #2 specimens of Example 23 weretested by a color difference meter (Tokyo Denshoku) to measure a colordifference. In compliance with the Japanese Industrial Standard (JIS)H0201, the color difference was indicated by the ΔE* index. Thevariation in the color difference after mounting to the acceleratedfouling test apparatus is shown in Table 7. TABLE 7 Striped AreaBackground #1 Specimen 4.1 1.1 #2 Specimen 0.8 0.5

[0253] As will be noted from Table 7, in the #1 specimen void of thephotocatalytic coating, a large amount of smudge was caused to adhere tothe vertical striped area corresponding to the flow path of rainwater,as compared with the #2 specimen provided with the photocatalyticcoating. It will also be recognized that, between the #2 and #1specimens, there was a substantial difference in the degree of foulingof the background area.

Example 25 Cleansing Capability for Oil Stains

[0254] A quantity of oleic acid was applied on the surface of the #1 and#3 specimens of Example 23, respectively, and the specimens were thenimmersed in water in a cistern with the specimen surface held in ahorizontal position. In the #1 specimen, oleic acid remained adhered tothe specimen surface. In contrast, in the #3 specimen, oleic acid becamerounded to form oil droplets which were then released from the surfaceof the specimen to rise to the top of the water.

[0255] In this manner, it was confirmed that, in the case that thesurface of a substrate was coated with a photocatalytic top coating, thesurface was maintained hydrophilic so that, when soaked in water, oilystains were readily released away from the surface whereby the surfacewas cleansed.

[0256] This Example illustrates that a tableware, for instance, fouledby oil or fat can be readily cleansed only by soaking it in waterwithout recourse to a detergent, provided that the surface thereof isprovided with a photocatalytic coating and if the photocatalyst isphotoexcited by UV irradiation.

Example 26 Drying of Water Wet Surface

[0257] The surface of the #1 and #3 specimens of Example 23 were wettedwith water and the specimens were left outdoors on a fair day to subjectthem to natural drying. The ambient temperature was about 25° C. As the#1 specimen was inspected 30 minutes later, water droplets stillremained on the surface. In contrast, it was found that the surface ofthe #3 specimen was completely dried.

[0258] It is considered that in the #3 specimen provided with thephotocatalytic coating, the adherent water droplets were caused tospread into a uniform film of water and for this reason drying wasaccelerated.

[0259] This Example illustrates the possibility that an eyeglass lens orautomotive windshield wetted with water may be promptly dried.

Example 27 Tile with Highly Hydrophilic Surface—Coating of SinteredTitania and Silica

[0260] A sol of the anatase form of titania (Ishihara Industries ofOsaka, STS-11) and a sol of colloidal silica (Nissan Chemical Ind.,“Snowtex O”) were admixed at a ratio by mol of 88:12 in terms of solidmatter and the mixture was applied by spray coating on the surface of aglazed tile (Toto Ltd., AB02E01) of 15 cm square in size, followed bysintering for 1 hour at a temperature of 800° C. to obtain a specimencovered by a coating comprised of titania and silica. The thickness ofthe coating was 0.3 μm. The contact angle with water immediately aftersintering was 5°.

[0261] The specimen was kept in the dark for a week but the contactangle measured thereafter was still 5°.

[0262] As the specimen surface was subjected to irradiation with UVlight for 1 day, at a UV intensity of 0.03 mW/cm² by using a BLBfluorescent lamp, the contact angle with water became 0°.

Example 28 Coating of Sintered Titania and Silica—Hydrophilificationunder Room Light

[0263] A sol of the anatase form of titania (STS-11) and a sol ofcolloidal silica (Nissan Chemical Ind., “Snowtex 20”) were admixed at aratio by mol of 80:20 in terms of solid matter and the mixture wasapplied by spray coating on the surface of a 15 cm-square glazed tile(AB02E01), followed by sintering for 1 hour at a temperature of 800° C.to obtain a specimen covered by a coating comprised of titania andsilica. The thickness of the coating was 0.3 μm. The contact angle withwater immediately after sintering was 5°.

[0264] The contact angle with water as measured after keeping thespecimen in the dark for 2 weeks was 14°.

[0265] As the specimen surface was subjected to irradiation with UVlight for 1 day, at a UV intensity of 0.004 mW/cm² by a whitefluorescent lamp, the contact angle with water became 4°.

[0266] Accordingly, it was found that the photocatalytic coating wasrendered hydrophilic to a satisfactory degree even under indoorillumination.

Example 29 Coating of Sintered Titania and Silica—Silica Content

[0267] A sol of the anatase form of titania (STS-11) and a sol ofcolloidal silica (Nissan Chemical Ind., “Snowtex 20”) were admixed at avarying ratio to obtain a plurality of suspensions having a ratio by molof silica to the solid matter of the suspension of 0%, 5%, 10%, 15%,20%, 25% and 30%, respectively. 0.08 g of each suspension was uniformlyapplied by spray coating on the surface of a 15 cm-square glazed tile(AB02E01) and each tile was fired for 1 hour at a temperature of 800° C.to obtain a plurality of specimens each covered by a coating comprisedof titania and silica.

[0268] The contact angle with water immediately after sintering of therespective specimens was as shown in the graph of FIG. 12. As will beapparent from the graph of FIG. 12, the initial contact angle waslowered by addition of silica.

[0269] The contact angle with water as measured after keeping thespecimen in the dark for 8 days was plotted in the graph of FIG. 13. Aswill be noted by comparing the graph of FIG. 12 with the graph of FIG.13, the loss of hydrophilicity resulting from keeping the specimens inthe dark is small in the specimens containing more than 10%, in theratio by mol, of silica.

[0270] Thereafter, the specimens were subjected to irradiation with UVlight for 2 days, at a UV intensity of 0.03 mW/cm² by using a BLBfluorescent lamp. The contact angle with water after irradiation isshown in the graph of FIG. 14. It will be noted from the graph that uponUV irradiation hydrophilicity is readily recovered in the case wheresilica is added to titania.

[0271] Then the specimens were kept in the dark for further 8 days andthe contact angle with water was measured. The results are shown in FIG.15. It will be noted from the graph that the loss of hydrophilicityresulting from keeping the specimens in the dark after UV irradiation issmall in the case where silica is added to titania.

[0272] A pencil scratch test was carried out to examine the abrasionresistance of the sintered film comprised of titania and silica. Theresults are shown in the graph of FIG. 16. It will be understood thatthe abrasion resistivity is increased with increasing silica content.

Example 30 Sludge Test

[0273] A mixture of a sol of the anatase form of titania (STS-11) and asol of colloidal silica (Snowtex 20) and having a silica content of 10%by weight in terms of solid matter was applied to a 15 cm-square glazedtile (AB02E01) in an amount of 4.5 mg in terms of solid matter and thetile was then calcined for 10 minutes at a temperature of 880° C. Thespecimen was then subjected to irradiation with UV light for 3 hours, ata UV intensity of 0.5 mW/cm² by using a BLB fluorescent lamp to obtain#1 specimen. The contact angle with water of the #1 specimen and theglazed tile (AB02E01) as such was 0° and 30°, respectively.

[0274] A mixture of powders of 64.3% by weight of yellow ochre, 21.4% byweight of calcined Kanto loam clay, 4.8% by weight of hydrophobic carbonblack, 4.8% by weight of silica powder, and 4.7% by weight ofhydrophilic carbon black was suspended in water at a concentration of1.05 g/l to prepare a slurry.

[0275] 150 ml of the thus prepared slurry was caused to flow down alongthe surface of the #1 specimen and the glazed tile (AB02E01) heldinclined at 45°, followed by drying for 15 minutes, and 150 ml ofdistilled water was thereafter caused to flow down, followed by dryingfor 15 minutes, the cycle of the above-mentioned sequences beingrepeated for 25 times. A change in color difference and in glossinessafter the sludge test was measured. The measurement of the glossinesswas carried out according to the method laid down by the JapaneseIndustrial Standard (JIS) Z8741 and the variation in the glossiness wasobtained by dividing the glossiness after testing by the glossinessbefore testing. The results are given in Table 8. TABLE 8 #1 SpecimenTile (AB02E01) Contact Angle (°) 0 30 Color Diff. Change 0.7 5.6Glossiness Change 93.4% 74.1%

Example 31 Relationship between Contact Angle with Water andSelf-cleaning and Antifouling Capability

[0276] Various specimens were subjected to a sludge test in a mannersimilar to Example 30. The tested specimens included the #1 specimen ofExample 30, #2 specimen having a copper-doped titania coating, theglazed tile (AB02E01), an acrylic resin plate, an artificial marbleplate (Toto Ltd., ML03) made of polyester resin matrix, and apolytetrafluoroethylene (PTFE) plate. The #2 specimen was prepared byspray coating 0.3 g of an aqueous solution of copper acetate monohydratehaving a copper concentration of 50 μmol/g on the #1 specimen of Example30 and, after drying, subjecting the specimen to irradiation with UVlight for 10 minutes, at a UV intensity of 0.4 mW/cm² by a BLBfluorescent lamp to thereby subject copper acetate monohydrate tophotoreduction deposition. The results of the sludge test are shown inTable 9. TABLE 9 Contact Angle Color Difference Glossiness Specimen withWater (°) Change Change (%) #1 Specimen 0.0 0.7 93.8 #2 Specimen 4.0 2.081.5 Glazed Tile 19.4 4.6 68.3 Acrylic Plate 50.9 4.5 69.3 Artif. Marble54.8 3.2 85.2 PTFE Plate 105.1 0.9 98.2

[0277] Furthermore, various specimens were subjected for a period of amonth to an accelerated fouling test similar to Example 23. Thespecimens used included the #1 specimen of Example 30, the glazed tile(AB02E01), an acrylic resin plate, an aluminum plate covered by a basecoating of silicone in a manner similar to Example 13, and a PTFE plate.The results of the accelerated tests are shown in Table 10 wherein,similar to Example 24, the change in the color difference representsthat of the vertical striped area of the specimens. TABLE 10 ContactAngle with Color Difference Specimen Water (°) Change #1 Specimen 0.00.9 Glazed Tile 19.4 1.5 Acrylic Plate 50.9 2.3 Silicone Coated 90.0 4.2PTFE Plate 105.1 7.8

[0278] To facilitate understanding, the contact angle with water as wellas the variation in the color difference are plotted in the graph ofFIG. 17. In the graph of FIG. 17, the curve A indicates the relationshipbetween the contact angle with water and the color difference changecaused by the contaminants such as airborne combustion products likecarbon black and city grime as a result of the accelerated fouling test,with the curve B representing the relationship between the contact anglewith water and the color difference change caused by sludge as a resultof the sludge test.

[0279] Referring to the graph of FIG. 17, as the contact angle withwater of the substrate increases, the dirt or stain due to combustionproducts and city grime becomes more conspicuous, as will be readilyunderstood from the curve A. This is because the contaminants such ascombustion products and city grime are generally hydrophobic and, hence,are apt to adhere to a hydrophobic surface.

[0280] In contrast, the curve B illustrates that the dirt or stain dueto sludge peaks when the contact angle with water is in the range of20-50°. This is because the inorganic substances such as loam and soilinherently have a hyrdophilicity on the order of 20-50° in terms of thecontact angle with water so that they are apt to adhere to a surfacehaving a similar hyrdophilicity. It will therefore be understood that,by rendering the surface hyrdophilic to the degree that the contactangle with water is less than 20° or, alternatively, by rendering thesurface hyrdophobic to the degree that the contact angle with water isgreater than 60°, the adherence of the inorganic substances to a surfacecan be prevented.

[0281] The reason why fouling by sludge is reduced as the contact anglewith water is less than 20° is that, when the surface is rendered highlyhydrophilic to the degree that the contact angle with water becomes lessthan 200, the affinity of the surface for water exceeds the affinity forinorganic substances so that adherence of inorganic substances isblocked by water which preferentially adheres to the surface and anyinorganic substances that have adhered to or are tending to adhere tothe surface are readily washed away by water.

[0282] It will be noted from the foregoing that, in order to preventboth the hydrophobic and hydrophilic substances from adhering to thesurface of a building and the like, or in order to ensure that dirt orsmudge deposited on the surface is washed away by rain water so as topermit the surface to be self-cleaned, it is desirable to modify thesurface to present a contact angle with water of less than 20 ,preferably less than 10°, more preferably less than 5°.

Example 32 Coating of Sintered Titania and Tin Oxide—Glazed Tile

[0283] A sol of the anatase form of titania (STS-11) and a sol of tinoxide (Taki Chemical K.K. of Kakogawa City, Hyogo-Prefecture; meancrystallite size of 3.5 nm) were admixed at various blending ratio(percent by weight of tin oxide to the sum of titania plus tin oxide)shown in Table 11 and the mixtures were applied by spray coating on thesurface of 15 cm-square glazed tiles (AB02E01), followed by sinteringfor 10 minutes at a temperature either of 750° C. or 800° C. to obtain#1-#6 specimens. After sintering, the #2, #4, #5 and #6 specimens werefurther doped with silver by applying thereon an aqueous solutioncontaining 1 weight percent of silver nitrate and by subjecting silvernitrate to photoreduction deposition. In addition, #7-#9 specimens werefurther prepared by applying onto the glazed tiles only a sol of tinoxide or a sol of titania and by sintering. After sintering, the #7 and#9 specimens were further doped with silver.

[0284] Each specimen was kept in the dark for a week and was thereaftersubjected to irradiation with UV light for 3 days, at a UV intensity of0.3 mW/cm² by using a BLB fluorescent lamp whereupon the contact anglewith water was measured. The results are shown in Table 11. TABLE 11SnO₂ Ratio Sintering Contact Specimen (wt %) Temp. (° C.) Ag Angle (°)#1 1 800 None 0 #2 5 800 Added 0 #3 15 800 None 0 #4 15 750 Added 0 #550 750 Added 0 #6 95 800 Added 5 #7 100 750 Added 8 #8 0 800 None 11 #90 800 Added 14

[0285] As will be apparent from Table 11, in the #8 and #9 specimenswhich were coated only with titania, the contact angle with waterexceeded 10°. This is because the alkaline network-modifier ions such assodium ions diffused from the glaze into the titania coating duringsintering whereby the photocatalytic activity of anatase was hindered.In contrast, it will be noted that, in the #1-#6 specimens wherein SnO₂were blended, the surface was hydrophilified to a high degree. As shownby the #7 specimen, tin oxide which is a semiconductor photocatalyst iseffective in rendering the surface hydrophilic in a manner similar totitania. Although the reason therefor is not clear, this Exampleillustrates that the effect of diffusion of the alkalinenetwork-modifier ions can be overcome by adding tin oxide to titania.

Example 33 Sintered Titania coating and Diffusion PreventionLayer—Glazed Tile

[0286] Tetraethoxysilane (marketed by Colcoat, “Ethyl 28”) was appliedby spray coating on the surface of a 15 cm-square glazed tile (AB02E01)which was then held at a temperature of about 150° C. for about 20minutes to subject tetraethoxysilane to hydrolysis and dehydrationpolymerization whereby a coating of amorphous silica was formed on thesurface of the glazed tile.

[0287] Then, a sol of the anatase form of titania (STS-11) was appliedby spray coating on the surface of the tile which was then fired for anhour at a temperature of 800° C.

[0288] The thus obtained specimen, as well as the #8 specimen of Example32 tested for the purposes of comparison, were kept in the dark for aweek and were then subjected to irradiation with UV light for 1 day, ata UV intensity of 0.3 mW/cm² by using a BLB fluorescent lamp whereuponthe contact angle with water was measured.

[0289] In contrast to the contact angle with water being 12° in the #8specimen of Example 32, the specimen provided with the intervening layerof amorphous silica was hydrophilified to the degree that the contactangle with water became less than 3°. It is therefore considered thatthe layer of amorphous silica is effective in preventing diffusion ofthe alkaline network-modifier ions being present in the glaze layer.

Example 34 Amorphous Titania Calcination Coating and DiffusionPrevention Layer—Glazed Tile

[0290] In a manner similar to Example 1, a thin film of amorphous silicaand then a thin film of amorphous titania were formed in sequence on thesurface of a 15 cm-square glazed tile (AB02E01). The tile was thencalcined at a temperature of 500° C. to transform amorphous titania intothe anatase form titania.

[0291] The specimen thus obtained was kept in the dark for several daysand was then subjected to irradiation with UV light for 1 day, at a UVintensity of 0.5 mW/cm² by using a BLB fluorescent lamp. The contactangle with water of the resultant specimen as measured was 0°. Similarto Example 33, it is considered that the layer of amorphous silica iseffective in rendering the surface of a tile highly hydrophilic.

Example 35 Glazed Tile—Cleansing Capability for Oil Stains

[0292] A quantity of oleic acid was applied on the surface of the #1specimen of Example 30. When the specimen was then immersed in water ina cistern with the specimen surface held in a horizontal position, oleicacid became rounded to form oil droplets which were then released fromthe surface of the tile to ascend to the top of the water.

[0293] This Example also illustrates that a surface of pottery, such astile and tableware, fouled by oil or fat can be readily cleansed merelyby soaking the object in water or by wetting it with water, providedthat the surface thereof is provided with a photocatalytic coating andprovided that the photocatalyst is photoexcited by UV irradiation.

Example 36 Glass—Cleansing Capability for Oil Stains

[0294] In a manner similar to Example 1, a thin film of amorphous silicaand then a thin film of amorphous titania were formed in sequence on thesurface of a 10 cm-square soda-lime glass plate. The glass plate wasthen fired at a temperature of 500° C. to transform amorphous titaniainto the anatase form titania.

[0295] A quantity of oleic acid was applied on the surface of the glassplate. As the glass plate was then immersed in water in a cistern withthe surface held in a horizontal position, oleic acid became rounded toform oil droplets which were then released from the surface of the glassplate and floated.

Example 37 Glass—Self-cleaning and Antifouling Capability

[0296] The specimen of Example 36 was subjected for a month to anaccelerated fouling test similar to Example 23. When inspected by theeye a month later, no smudge of a vertically striped pattern wasobserved.

Example 38 Glazed Tile—Antibacterial Enhancer (Ag Doping)

[0297] A coating comprised of titania and silica was formed on thesurface of a 15 cm-square glazed tile (AB02E01) in a manner similar toExample 27.

[0298] Then an aqueous solution containing 1 weight percent of silverlactate was applied onto the surface of the tile which was thensubjected to irradiation with UV light of a BLB fluorescent lamp tothereby subject silver lactate to photoreduction to form a silverdeposit whereby a specimen coated with silver doped titania wasobtained. The contact angle with water as measured was 0°.

[0299] When the tile was then tested for the antibacterial function in amanner similar to Example 19, the survival rate of colibacillus was lessthan 10%.

Example 39 Glazed Tile—Antibacterial Enhancer (Cu Doping)

[0300] A coating comprised of titania and silica was formed on thesurface of a 15 cm-square glazed tile (AB02E01) in a manner similar toExample 27.

[0301] Then an aqueous solution containing 1 weight percent of copperacetate monohydrate was applied onto the surface of the tile which wasthen subjected to irradiation with UV light of a BLB fluorescent lamp tothereby subject copper acetate monohydrate to photoreduction to form acopper deposit whereby a specimen coated with copper-doped titania wasobtained. The contact angle with water as measured was less than 3°.

[0302] As the tile was then tested for the antibacterial function in amanner similar to Example 19, the survival rate of colibacillus was lessthan 10%.

Example 40 Glazed Tile—Photo-redox Activity Enhancer

[0303] A coating comprised of titania and silica was formed on thesurface of a 15 cm-square glazed tile (AB02E01) in a manner similar toExample 27.

[0304] Then, the surface of the specimen was doped with platinum in amanner similar to Example 22. The contact angle with water as measuredwas 0°.

[0305] The removal rate of methyl mercaptan as measured in a mannersimilar to Example 20 was 98%.

Example 41 Effect of Photoexciting Wavelength

[0306] After being kept in the dark for 10 days, the #8 specimen ofExample 32 and, for the purposes of comparison, the glazed tile(AB02E01) without titania coating were subjected to irradiation with UVlight by using a Hg—Xe lamp under the conditions shown in Table 12 andon doing so the variation in response to time of the contact angle withwater was measured. TABLE 12 UV Wavelength UV Intensity Photon Density(nm) (mW/cm²) (photon/sec/cm²) 313 10.6 1.66 × 10¹⁶ 365 18 3.31 × 10¹⁶405 6 1.22 × 10¹⁶

[0307] The results of measurement were shown in FIGS. 18A-18C whereinthe value plotted by white dots represents the contact angle with waterof the #8 specimen of Example 32 and the value plotted by black dotsindicates the contact angle with water of the glazed tile which was notprovided with the titania coating.

[0308] As will be understood from FIG. 18C, hydrophilification did notoccur in the case that a UV light having an energy lower than that of awavelength of 387 nm corresponding to the bandgap energy of the anataseform of titania (i.e., a UV light having a wavelength longer than 387nm) was irradiated.

[0309] In contrast, as will be apparent from FIGS. 18A and 18B, thesurface was rendered hydrophilic upon irradiation with UV light havingan energy higher than the bandgap energy of anatase.

[0310] From the foregoing, it was confirmed that hydrophilification of asurface would not occur unless the photocatalyst is photoexcited andthat hydrophilification of a surface results from the photocatalyticaction of the photocatalyst.

Example 42 Physisorption of Water under Photocatalytic Action

[0311] Powders of the anatase form of titania (made by Nihon Aerosol,P-25) were pressed to form three specimens in the form of a disc ofcompacted powders. The specimens were subjected respectively toExperiments 1-3, described below, wherein the surface of the specimenswas tested and inspected by the Fourier transform infrared spectroscopicanalysis (FT-IR) using a Fourier transform infrared spectrometer(FTS-40A). Throughout these experiments, an ultraviolet lamp (UVL-21)having a wavelength of 366 nm was used for UV irradiation.

[0312] For the purpose of analyzing the infrared absorption spectrum,the following absorption bands are assigned, respectively, to thefollowing information.

[0313] Sharp absorption band at wavenumber 3690 cm⁻¹:

[0314] stretching of OH bond of chemisorbed water.

[0315] Broad absorption band at wavenumber 3300 cm⁻¹:

[0316] stretching of OH bond of physisorbed water.

[0317] Sharp absorption band at wavenumber 1640 cm⁻¹:

[0318] bending of HOH bond of physisorbed water.

[0319] Absorption bands at wavenumbers 1700 cm⁻¹, 1547 cm⁻¹, 1475 cm⁻¹,1440 cm¹, and 1365 cm⁻¹:

[0320] carbonyl groups of contaminants adsorbed onto the specimensurface.

[0321] Experiment 1

[0322] First, the titania disc immediately after press forming wassubjected to the infrared spectroscopic analysis. The absorptionspectrum of the disc immediately after press forming is shown by thecurve #1 in the graphs of FIGS. 19A and 19B.

[0323] After keeping the titania disc for 17 hours in a dry boxcontaining silica gel as a desiccant, the absorption spectrum wasdetected which is indicated by the curve #2 in the graphs of FIGS. 19Aand 19B. As will be understood upon comparison of the #1 spectrum withthe #2 spectrum, infrared absorption at the wavenumber 3690 cm⁻¹ wasdrastically decreased in the #2 spectrum, indicating that chemisorbedwater has decreased. Similarly, absorption at the wavenumbers 3300 and1640 cm⁻¹ was drastically decreased in the #2 spectrum, indicating thatphysisorbed (physically adsorbed) water has also decreased. It istherefore observed that both chemisorbed water and physisorbed waterhave decreased by keeping the specimen in dry air for 17 hours.

[0324] In contrast, infrared absorption at wavenumber 1300-1700 cm⁻¹ dueto presence of the carbonyl groups was increased, suggesting that,during storage of the specimen, compounds containing carbonyl groupswere adsorbed onto the specimen surface thereby contaminating thesurface. It was impossible to measure the variation in the contact anglewith water at the surface of the specimen because of the porous natureof surface of the disc-shaped specimen which was made by press-formingof titania powders. However, it is presumed that the contact angle withwater at the surface of a specimen would be increased during storage indry air if the specimen were made in the form of a thin film of theanatase form of titania.

[0325] Then, the titania disc in the dry box was subjected toirradiation with UV light for an hour, at a UV intensity of 0.5 mW/cm²and the absorption spectrum was detected which is shown in the graphs ofFIGS. 19A and 19B by the curve #3.

[0326] As will be apparent from the #3 spectrum, absorption atwavenumber 3690 cm⁻¹ was almost revived. Similarly, absorption atwavenumbers 3300 and 1640 cm⁻¹ substantially restored the initial level.It is therefore observed that, upon UV irradiation, both the amount ofchemisorbed water and the amount of physisorbed water are resumed theinitial level. It is presumed that, if the specimen were made in theform of a titania thin film, the surface of the thin film would berendered hydrophilic upon UV irradiation so that the contact angle withwater would be decreased.

[0327] Thereafter, the specimen was placed for 24 hours in a dark roomcommunicated with the ambient air and the absorption spectrum wasdetected. To avoid various curves being overly complicated, the detectedabsorption spectrum is shown in the different graphs of FIGS. 20A and20B by the curve #4. Further, to provide a basis for comparison, the #2spectrum is reproduced in the graphs of FIGS. 20A and 20B.

[0328] As shown by the #4 curve, a slight decrease is observed in theabsorption at wavenumbers 3690 and 1640 cm⁻¹. Accordingly, it isconcluded that the amount of chemisorbed and physisorbed water slightlydecreases as the specimen after UV irradiation is placed in the dark inthe presence of moisture in the ambient air. However, absorption atwavenumber 1300-1700 cm⁻¹ is increased, showing that carbonyl compoundswere further adsorbed. It is presumed that, if the specimen were made inthe form of a titania thin film, the contact angle with water would beincreased in response to contamination.

[0329] Finally, the titania disc was again subjected to irradiation withUV light in a dark room communicated with the ambient air for an hour,at a UV intensity of 0.5 mW/cm² and the absorption spectrum was detectedwhich is shown in the graphs of FIGS. 20A and 20B by the curve #5. Asshown in the graphs, no change was observed in the absorption atwavenumber 3690 cm⁻¹, whereas the absorption at wavenumber 3300 cm⁻¹ isremarkably increased, with the absorption at wavenumber 1640 cm⁻¹ beingincreased. It will therefore be noted that as a result of re-irradiationwith UV light, the amount of chemisorbed water remained unchanged butthe amount of water was increased. It is presumed that, if the specimenwere made in the form of a titania thin film, the contact angle withwater would be decreased upon UV irradiation.

[0330] Experiment 2

[0331] First, the titania disc immediately after press forming wassubjected to the infrared spectroscopic analysis. The absorptionspectrum detected is shown in the graphs of FIGS. 21A and 21B by thecurve #1.

[0332] Then, the titania disc was subjected to irradiation with UV lightfor one hour, at a UV intensity of 0.5 mW/cm² and the absorptionspectrum was detected which is shown in the graphs of FIGS. 21A and 21Bby the curve #2.

[0333] The disc was further subjected to irradiation with UV light atthe same UV intensity for additional one hour (total 2 hours), furtheradditional one hour (total 3 hours), and further additional 2 hours(total 5 hours) and the absorption spectra detected at the end ofirradiation are shown in FIGS. 22A and 22B by the curve #3, #4 and #5,respectively.

[0334] As will be understood upon comparison of the #1 spectrum with the#2 spectrum, both the amount of chemisorbed water and the amount ofphysisorbed water were increased as the disc was subjected for the firsttime to UV irradiation. During the first irradiation, the amount ofadherent carbonyl compounds was slightly increased. Presumably, thecontact angle with water would be decreased in response to UVirradiation if the specimen were made in the form of a titania thinfilm.

[0335] After the disc was subjected to UV irradiation for further onehour (total 2 hours), the amount of chemisorbed water was slightlydecreased but the amount of physisorbed water remained unchanged, asshown by the #2 and #3 spectra. The amount of adherent carbonylcompounds was slightly increased. It is considered that the absence ofany change in the amount of physisorbed water is due to saturation ofthe physisorbed water. It is presumed that the contact angle with waterwould remain unchanged if the specimen were made in the form of atitania thin film.

[0336] As will be noted from the #4 and #5 spectra, UV irradiation forfurther one hour (total 3 hours) and for further 2 hours (total 5 hours)resulted in a further slight decrease in the amount of chemisorbedwater, with the amount of physisorbed water remained unchanged. Theamount of adhered carbonyl compounds was increased. It is consideredthat the contact angle with water would remain unchanged if the UVirradiation were carried out on a specimen made in the form of a titaniathin film.

[0337] Experiment 3

[0338] This experiment is similar to Experiment 1 in many respects andthe major difference resides in that the UV intensity was decreased.

[0339] First, the titania disc immediately after press forming wassubjected to the infrared spectroscopic analysis. The detectedabsorption spectrum is shown by the curve #1 in the graphs of FIGS. 23Aand 23B. Then, the disc was placed for 34 hours in a dark roomcommunicated with the ambient air and thereafter the absorption spectrumwas detected which is shown by the curve #2 in the graphs of FIGS. 23Aand 23B. Then, the titania disc placed in the same dark room wassubjected to irradiation with UV light for 2 hours, at a UV intensity of0.024 mW/cm² and the absorption spectrum was detected, the detectedspectrum being indicated by the curve #3 in the graphs of FIGS. 23A and23B.

[0340] As will be understood from the graphs, both the amount ofchemisorbed water and the amount of physisorbed water were decreased asthe disc was placed in a dark room in the presence of ambient moisture.As the amount of carbonyl compounds adhered to the specimen wasincreased, it is presumed that the contact angle with water would beincreased if a specimen made in the form of a titania thin film wereused.

[0341] It will be noted that in response to UV irradiation the amount ofchemisorbed water was slightly increased and the amount of physisorbedwater was increased to again attain to the initial level. During UVirradiation, the amount of adherent carbonyl compounds was slightlyincreased. It is presumed that the contact angle with water would beincreased during UV irradiation if a specimen made in the form of atitania thin film were used.

[0342] Evaluation of the Test Results

[0343] To facilitate comparison, the results of Experiments 1-3 aresummarized in Table 13 below. TABLE 13 Contact Chemisorbed PhysisorbedCarbonyl Experiment Angle w/w Water Water Compound Experiment 1 (0.5mW/cm²) -dark room increased decreased decreased increased dry air -UVirradiated decreased almost restored decreased dry air restored -darkroom increased slightly slightly increased ambient air decreaseddecreased -UV irradiated decreased unchanged increased unchanged ambientair Experiment 2 (0.5 mW/cm²) -UV irradiated decreased slightlyincreased slightly (1 h) increased increased -UV irradiated unchangedslightly unchanged slightly (2 h) decreased increased -UV irradiatedunchanged slightly unchanged increased (3 h) decreased -UV irradiatedunchanged slightly unchanged increased (5 h) decreased Experiment 3(0.024 mW/cm²) -dark room increased decreased decreased increasedambient air -UV irradiated decreased slightly increased increasedambient air increased

[0344] As will be best understood from Table 13, the amount ofphysisorbed water increases in good response to UV irradiation.

[0345] In this regard, it is considered that, as illustrated in theupper part of FIG. 24, in the crystal face of a crystal of titaniaforming a titania coating 30, a terminal OH group 32 is bonded to eachtitanium atom, with a bridging OH group 34 being bonded to a pair ofadjacent titanium atoms, these OH groups 32 and 34 forming a layer ofchemisorbed water. It is considered that, upon irradiation with UV lightin the presence of ambient moisture, molecules of water in the ambientair are physically adsorbed by way of hydrogen bond 36 onto the hydrogenatoms of the terminal and bridging OH groups to thereby form a layer ofphysisorbed water 38, as illustrated in the lower part of FIG. 24.

[0346] As the amount of physisorbed water increases in good response toUV irradiation as described before, Example 42 demonstrates thatformation of a layer of physisorbed water 38 is induced by thephotocatalytic action of titania. It is believed that because of thepresence of the layer of physisorbed water 38 the surface of titaniasurface is rendered hydrophilic.

[0347] In contrast, the amount of carbonyl compounds adhered to thesurface appears to increase with increasing duration of contact withambient air. It is considered that upon photoexcitation of thephotocatalyst the water-wettability of the surface is increasedregardless of increasing amount of adherent carbonyl compounds.

Example 43 Plastic Plate Coated by Photocatalyst-containing Silicone

[0348] A titania-containing coating composition similar to that ofExample 18 was applied on a polyethyleneterephthalate (PET) film (FujiXerox, monochromatic PPC film for OHP, JF-001) and was cured at atemperature of 110° C. to obtain #1 specimen coated withtitania-containing silicone.

[0349] Further, an aqueous polyester paint (made by Takamatsu Resin,A-124S) was applied on another PET film (JF-001) and was cured at 10° C.to form a primer coating. A titania-containing coating compositionsimilar to that of Example 18 was then applied on the primer coating andwas cured at a temperature of 110° C. to obtain #2 specimen.

[0350] Also, a titania-containing coating composition similar to that ofExample 18 was applied on a polycarbonate (PC) plate and was cured at atemperature of 110° C. to obtain #3 specimen.

[0351] Furthermore, an aqueous polyester paint (A-124S) was applied onanother polycarbonate plate, followed by curing at a temperature of 110°C. to form a primer coating, and a titania-containing coatingcomposition similar to that of Example 18 was thereafter applied thereonfollowed by curing at a temperature of 110° C. to obtain #4 specimen.

[0352] The #1-#4 specimens as well as the PET film (JF-001) andpolycarbonate plate as such were subjected to irradiation with UV light,at a UV intensity of 0.6 mW/cm² by using a BLB fluorescent lamp and ondoing so the variation in response to time of the contact angle withwater of the specimen surface was measured. The results are shown inTable 14. TABLE 14 Before 1 day 2 days 3 days 10 days Specimen Irradiat.later later later later #1 71° 44° 32°  7°  2° #2 73° 35° 16°  3°  2° #366° 55° 27°  9°  3° #4 65° 53° 36° 18°  2° PET 70° 72° 74° 73° 60° PC90° 86° 88° 87° 89°

[0353] As will be apparent from Table 14, the surface of the specimensunder question was hydrophilified as UV irradiation was continued andabout 3 days later the surface is rendered superhydrophilic. Asdescribed hereinbefore with reference to Example 14, it is consideredthat this is due to the fact that the organic groups bonded to thesilicon atoms of the silicone molecules of the titania-containingsilicone layer were substituted with the hydroxyl groups under thephotocatalytic action caused by photoexcitation.

[0354] As is well-known, a UV intensity of 0.6 mW/cm² is roughly equalto the intensity of the UV light contained in the sunlight impingingupon the earth's surface. It will be noted, accordingly, thatsuperhydrophilification can be achieved simply by exposing thetitania-containing silicone coating to the sunlight.

Example 44 Weathering Test of Photocatalyst-containing Silicone

[0355] The #1 specimen (aluminum substrate coated with silicone) and the#2 specimen (aluminum substrate coated with titania-containing silicone)of Example 13 were subjected to a weathering test by using a weatheringtesting machine (made by Suga Testing Instruments, Model “WEL-SUN-HC”)while irradiating a light from a carbon arc lamp and spraying rain for12 minutes per hour and at a temperature of 40° C. The weatherresistivity was assessed by the glossiness retention rate (percentage ofthe glossiness after testing to the initial glossiness). The results areshown in Table 15. TABLE 15 Specimen 500 hrs 1000 hrs 3000 hrs #1 91 9590 #2 99 100 98

[0356] As will be apparent from Table 15, the glossiness retention rateremained roughly the same regardless of the presence or absence oftitania. This indicates that the siloxane bonds forming the main chainof the silicone molecule were not broken by the photocatalytic action oftitania. It is therefore considered that the weather resistivity ofsilicone is not affected even after the organic groups bonded to thesilicon atoms of the silicone molecules are substituted with thehydroxyl groups.

[0357] While the present invention has been described herein withreference to the specific embodiments thereof, it is contemplated thatthe invention is not limited thereby and various modifications andalterations may be made therein without departing from the scope of theinvention. Furthermore, the present invention may be applied for variouspurposes and fields other than the aforesaid. For example, asuperhydrophilified surface may be utilized to prevent air bubbles fromadhering to an underwater surface. Also, the superhydrophilified surfacemay be used to form and maintain a uniform film of water. Moreover, inview of an excellent affinity for vital tissues and organs, thesuperhydrophilic photocatalytic coating may be utilized in the medicalfields such as contact lens, artificial organs, catheters, andanti-thrombotic materials.

1. A method for rendering a surface of a substrate hydrophilic,comprising the steps of: preparing a substrate coated with aphotocatalytic layer comprised of a photocatalyst; and, subjecting saidphotocatalyst to photoexcitation to thereby cause molecules of water tobe physically adsorbed onto the surface of said photocatalytic layerunder the photocatalytic action of the photocatalyst whereby the surfaceof the substrate is rendered hydrophilic.
 2. A composite with ahydrophilic surface, comprising: a substrate having a surface; aphotocatalytic layer comprised of a photocatalyst, said layer beingbonded to the surface of said substrate; and, molecules of waterphysically adsorbed onto the surface of said photocatalytic layer uponphotoexcitation of the photocatalyst.
 3. A coating composition for usein forming a photocatalytically hydrophilifiable coating on a substrate,said coating composition comprising a photocatalyst operable uponphotoexcitation thereof to cause molecules of water to be physicallyadsorbed onto the surface of said coating under the photocatalyticaction of the photocatalyst to thereby render the surface hydrophilic.4. A composite with a hydrophilic surface, comprising: a substratehaving a surface; and, a photocatalytic layer comprised of aphotocatalyst, said layer being bonded to the surface of said substrate;said photocatalyst operating upon photoexcitation thereof to render thesurface of said composite hydrophilic such that the surface of saidcomposite presents a water wettability of less than about 5° in terms ofthe contact angle with water.
 5. An antifogging transparent sheet membercomprising: a transparent substrate having a surface; and, asubstantially transparent photocatalytic layer comprised of aphotocatalyst, said photocatalytic layer being bonded to the surface ofsaid substrate; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic on the order ofless than about 5° in terms of the contact angle with water wherebyadherent moisture condensate and/or water droplets are caused to spreadover the surface of said layer to thereby prevent the substrate frombeing fogged or blurred with adherent moisture condensate and/or waterdroplets.
 6. An antifogging mirror comprising: a substrate having asurface and a reflective coating; and, a substantially transparentphotocatalytic layer comprised of a photocatalyst, said photocatalyticlayer being bonded to the surface of said substrate; said photocatalystoperating upon photoexcitation thereof to render the surface of saidlayer hydrophilic on the order of less than about 5° in terms of thecontact angle with water whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of said layer tothereby prevent the substrate from being fogged or blurred with adherentmoisture condensate and/or water droplets.
 7. An antifogging lenscomprising: a transparent lens-forming body having a surface; and, asubstantially transparent photocatalytic layer comprised of aphotocatalyst, said photocatalytic layer being bonded to the surface ofsaid lens-forming body; said photocatalyst operating uponphotoexcitation thereof to render the surface of said layer hydrophilicon the order of less than about 5° in terms of the contact angle withwater whereby adherent moisture condensate and/or water droplets arecaused to spread over the surface of said layer to thereby prevent thelens-forming body from being fogged or blurred with adherent moisturecondensate and/or water droplets.
 8. A composite according to claim 4,wherein said photocatalytic layer is resistant to adhesion by depositsand contaminants when contacted with an aqueous substance.
 9. Acomposite according to claim 8, wherein, for self-cleaning of thecomposite, said photocatalytic layer operates to permit adherentdeposits and/or contaminants to be washed away by rainwater as saidcomposite is subjected to rainfall.
 10. A composite according to claim8, wherein said photocatalytic layer operates to prevent contaminantsfrom adhering to the surface thereof as contaminant-laden rainwaterflows therealong.
 11. A composite according to claim 8, wherein, tofacilitate cleansing of the composite with water, said photocatalyticlayer operates to release adherent deposits and/or contaminants whensoaked in or wetted with water.
 12. A composite according to claim 4,wherein said photocatalytic layer is resistant to the formation of waterdroplets on the surface of said layer.
 13. A composite according toclaim 12, wherein, for prevention of growth of water droplets, saidphotocatalytic layer operates to cause adherent moisture condensateand/or water droplets to spread over the surface of said layer.
 14. Acomposite according to claim 12, wherein, to promote drying of thesubstrate after wetted with water, said photocatalytic layer operates tocause adherent water droplets to spread over the surface of said layer.15. A composite according to claim 4, wherein the surface of said layeris further coated with a hydrophilic protective layer.
 16. A compositeaccording to claim 4, wherein the surface of said layer is furthercoated with a photocatalytic protective layer which is adapted to berendered hydrophilic upon photoexcitation.
 17. A composite according toclaim 4, wherein said photocatalyst comprises an oxide selected from thegroup consisting of TiO₂, ZnO, SnO₂, SrTiO₃, WO₃, Bi₂O₃ and Fe₂O₃.
 18. Acomposite according to claim 4, wherein said photocatalyst comprises theanatase form of titania.
 19. A composite according to claim 4, whereinsaid photocatalyst comprises the rutile form of titania.
 20. A compositeaccording to claim 4, wherein said photocatalytic layer furthercomprises SiO₂ or SnO₂.
 21. A composite according to claim 4, whereinsaid photocatalytic layer comprises a coating in which particles of saidphotocatalyst are uniformly dispersed.
 22. A composite according toclaim 4, wherein said photocatalytic layer is comprised of siliconehaving organic groups bonded to silicon atoms of silicone molecules, andwherein the surface of said photocatalytic layer is formed of aderivative of silicone in which the organic groups bonded to the siliconatoms of the silicone molecules have been substituted uponphotoexcitation at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst.
 23. A composite accordingto claim 4, further comprising an intermediate layer of anon-decomposable material interleaved between said substrate and saidphotocatalytic layer.
 24. A composite according to claim 4, wherein saidsubstrate contains alkaline metal ions or alkaline-earth metal ions andwherein a thin film for preventing said ions from diffusing from saidsubstrate into said photocatalytic layer is interleaved between saidsubstrate and said photocatalytic layer.
 25. A composite according toclaim 24, wherein said thin film comprises silica.
 26. A compositeaccording to claim 4, wherein the thickness of said photocatalytic layeris less than about 0.2 micrometers.
 27. A composite according to claim4, wherein said photocatalytic layer further comprises a metal selectedfrom the group consisting of Ag, Cu and Zn.
 28. A composite according toclaim 4, wherein said photocatalytic layer further comprises a metalselected from the group consisting of Pt, Pd, Rh, Ru, Os and Ir.
 29. Amethod for rendering a surface of a substrate hydrophilic, comprisingthe steps of: preparing a substrate coated with a layer comprised of aphotocatalyst; and, subjecting said photocatalyst to photoexcitationuntil the surface of said layer presents a water-wettability of lessthan about 5° in terms of the contact angle with water.
 30. Anantifogging method for preventing a transparent sheet member from beingfogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: preparing a transparentsheet member coated with a substantially transparent layer comprised ofa photocatalyst; and, subjecting said photocatalyst to photoexcitationto thereby render the surface of said layer hydrophilic until thesurface of said layer presents a water-wettability of less than about 5°in terms of the contact angle with water whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer.
 31. An antifogging method for preventing a mirror frombeing fogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: preparing a mirror coatedwith a substantially transparent layer comprised of a photocatalyst;and, subjecting said photocatalyst to photoexcitation to thereby renderthe surface of said layer hydrophilic until the surface of said layerpresents a water-wettability of less than about 5° in terms of thecontact angle with water whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of said layer. 32.An antifogging method for preventing a lens from being fogged or blurredwith adherent moisture condensate and/or water droplets, said methodcomprising the steps of: preparing a lens coated with a substantiallytransparent layer comprised of a photocatalyst; and, subjecting saidphotocatalyst to photoexcitation to thereby render the surface of saidlayer hydrophilic until the surface of said layer presents awater-wettability of less than about 5° in terms of the contact anglewith water whereby adherent moisture condensate and/or water dropletsare caused to spread over the surface of said layer.
 33. A method forcleaning a substrate, comprising the steps of: preparing a substratecoated with a layer comprised of a photocatalyst; disposing saidsubstrate outdoors; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 5° interms of the contact angle with water; and, subjecting said substrate torainfall whereby deposits and/or contaminants adhering on the surface ofsaid layer are washed away by rainwater.
 34. A method for cleaning asubstrate, comprising the steps of: preparing a substrate coated with alayer comprised of a photocatalyst; subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the surface of said layer presents a water-wettability of lessthan about 5° in terms of the contact angle with water; and, rinsingsaid substrate with water whereby organic deposits and/or contaminantsadhering on the surface of said layer are released therefrom and washedaway by water.
 35. A method for cleaning a substrate, comprising thesteps of: preparing a substrate coated with a layer comprised of aphotocatalyst; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 5° interms of the contact angle with water; and, causing said substratesoaked in or wetted with water whereby organic deposits and/orcontaminants adhering on the surface of said layer are releasedtherefrom.
 36. A method for maintaining a surface of a substratedisposed outdoors clean, comprising the steps of: preparing a substratecoated with a layer comprised of a photocatalyst; disposing saidsubstrate outdoors; and, subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the surface of said layer presents a water-wettability of lessthan about 5° in terms of the contact angle with water wherebycontaminants are prevented from adhering to the surface of saidsubstrate as contaminant-laden rainwater flows therealong.
 37. A methodfor preventing growth of water droplets adhering on a substrate,comprising the steps of: preparing a substrate coated with a layercomprised of a photocatalyst; subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the surface of said layer presents a water-wettability of lessthan about 5° in terms of the contact angle with water; and, causingadherent moisture condensate and/or water droplets to spread over thesurface of said layer.
 38. A method according to one of claims 29-37,wherein the step of subjecting said photocatalyst to photoexcitation iscarried out with the sunlight.
 39. A method according to one of claims29-37, wherein the step of subjecting said photocatalyst tophotoexcitation is carried out with an electric lamp selected from thegroup consisting of fluorescent lamp, incandescent lamp, metal halidelamp, and mercury lamp.
 40. A method for rendering a surface of asubstrate hydrophilic, comprising the steps of: coating the surface ofthe substrate with a layer comprised of a photocatalyst; and, subjectingsaid photocatalyst to photoexcitation until the surface of said layerpresents a water-wettability of less than about 5° in terms of thecontact angle with water.
 41. An antifogging method for preventing atransparent sheet member from being fogged or blurred with adherentmoisture condensate and/or water droplets, said method comprising thesteps of: preparing a transparent sheet member; coating the surface ofsaid transparent sheet member with a substantially transparent layercomprised of a photocatalyst; and, subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the surface of said layer presents a water-wettability of lessthan about 5° in terms of the contact angle with water whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said layer.
 42. An antifogging method for preventing a mirrorfrom being fogged or blurred with adherent moisture condensate and/orwater droplets, said method comprising the steps of: preparing a mirror;coating the surface of said mirror with a substantially transparentlayer comprised of a photocatalyst; and, subjecting said photocatalystto photoexcitation to thereby render the surface of said layerhydrophilic until the surface of said layer presents a water-wettabilityof less than about 5° in terms of the contact angle with water wherebyadherent moisture condensate and/or water droplets are caused to spreadover the surface of said layer.
 43. An antifogging method for preventinga lens from being fogged or blurred with adherent moisture condensateand/or water droplets, said method comprising the steps of: preparing alens; coating the surface of said lens with a substantially transparentlayer comprised of a photocatalyst; and, subjecting said photocatalystto photoexcitation to thereby render the surface of said layerhydrophilic until the surface of said layer presents a water-wettabilityof less than about 5° in terms of the contact angle with water wherebyadherent moisture condensate and/or water droplets are caused to spreadover the surface of said layer.
 44. A method for cleaning a substrate,comprising the steps of: preparing a substrate; coating the surface ofsaid substrate with a layer comprised of a photocatalyst; disposing saidsubstrate outdoors; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 5° interms of the contact angle with water; and, subjecting said substrate torainfall whereby deposits and/or contaminants adhering on the surface ofsaid layer are washed away by rainwater.
 45. A method for cleaning asubstrate, comprising the steps of: preparing a substrate; coating thesurface of said substrate with a layer comprised of a photocatalyst;subjecting said photocatalyst to photoexcitation to thereby render thesurface of said layer hydrophilic until the surface of said layerpresents a water-wettability of less than about 5° in terms of thecontact angle with water; and, rinsing said substrate with water wherebyorganic deposits and/or contaminants adhering on the surface of saidlayer are released therefrom and washed away by water.
 46. A method forcleaning a substrate, comprising the steps of: preparing a substrate;coating the surface of said substrate with a layer comprised of aphotocatalyst; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 5° interms of the contact angle with water; and, causing said substratesoaked in or wetted with water whereby organic deposits and/orcontaminants adhering on the surface of said layer are releasedtherefrom.
 47. A method for maintaining a surface of a substratedisposed outdoors clean, comprising the steps of: preparing a substrate;coating the surface of said substrate with a layer comprised of aphotocatalyst; disposing said substrate outdoors; and, subjecting saidphotocatalyst to photoexcitation to thereby render the surface of saidlayer hydrophilic until the surface of said layer presents awater-wettability of less than about 5° in terms of the contact anglewith water whereby contaminants are prevented from adhering to thesurface of said substrate as contaminant-laden rainwater flowstherealong.
 48. A method for preventing growth of water dropletsadhering on a substrate, comprising the steps of: preparing a substratehaving a surface; coating the surface of said substrate with a layercomprised of a photocatalyst; subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the surface of said layer presents a water-wettability of lessthan about 5° in terms of the contact angle with water; and, causingadherent moisture condensate and/or water droplets to spread over thesurface of said layer.
 49. A method according to one of claims 40-48,wherein the step of subjecting said photocatalyst to photoexcitation iscarried out with the sunlight.
 50. A method according to one of claims40-48, wherein the step of subjecting said photocatalyst tophotoexcitation is carried out with an electric lamp selected from thegroup consisting of fluorescent lamp, incandescent lamp, metal halidelamp, and mercury lamp.
 51. A method of manufacturing a composite with ahydrophilic surface, comprising the steps of: preparing a substratehaving a surface; and, coating the surface of said substrate with aphoto-reactive layer comprised of a photocatalyst and operable topresent upon photoexcitation a water wettability of less than about 5°in terms of the contact angle with water.
 52. A method of manufacturingan antifogging transparent sheet member, comprising the steps of:preparing a transparent substrate having a surface; and, coating thesurface of said substrate with a substantially transparentphoto-reactive layer comprised of a photocatalyst and operable topresent upon photoexcitation a water wettability of less than about 5°in terms of the contact angle with water.
 53. A method of manufacturinga self-cleaning composite, comprising the steps of: preparing asubstrate having a surface; and, coating the surface of said substratewith a photo-reactive layer comprised of a photocatalyst and operable topresent upon photoexcitation a water wettability of less than about 5°in terms of the contact angle with water.
 54. A method of manufacturingan antifogging mirror, comprising the steps of: preparing a substratewith or without a reflective coating, said substrate having a surface;coating the surface of said substrate with a substantially transparentphoto-reactive layer comprised of a photocatalyst and operable topresent upon photoexcitation a water wettability of less than about 5°in terms of the contact angle with water; and, forming where necessary areflective coating on the opposite surface of said substrate prior to orsubsequent to or during the course of said step of coating.
 55. A methodof manufacturing an antifogging lens, comprising the steps of: preparinga lens-forming body having a surface; and, coating the surface of saidbody with a substantially transparent photo-reactive layer comprised ofa photocatalyst and operable to present upon photoexcitation a waterwettability of less than about 5° in terms of the contact angle withwater.
 56. A method according to one of claims 51-55, wherein said stepof coating comprises the substeps of: (a) coating the surface with athin film of amorphous titania; and, (b) heating said thin film at atemperature less than the softening point of the substrate to transformamorphous titania into crystalline titania.
 57. A method according toclaim 56, wherein prior to said substep (a) the substrate is coated witha thin film of silica to prevent alkaline network-modifier ions fromdiffusing from the substrate into said photocatalytic layer.
 58. Amethod according to claim 56, wherein said substep (a) is carried out byapplying onto the surface a solution of an organic compound of titanium,followed by subjecting said compound to hydrolysis and dehydrationpolymerization to form said thin film of amorphous titania over thesurface.
 59. A method according to claim 58, wherein said organiccompound of titanium is selected from the group consisting of analkoxide of titanium, a chelate of titanium and an acetate of titanium.60. A method according to claim 56, wherein said step (a) is carried outby applying onto the surface a solution of an inorganic compound oftitanium, followed by subjecting said compound to hydrolysis anddehydration polymerization to form said thin film of amorphous titaniaover the surface.
 61. A method according to claim 60, wherein saidinorganic compound of titanium is TiCl₄ or Ti(SO₄)₂.
 62. A methodaccording to claim 56, wherein said step (a) is carried out bysputtering.
 63. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising a photocatalyst operable upon photoexcitationthereof to render the surface of said coating hydrophilic on the orderof less than about 5° in terms of the contact angle with water.
 64. Acoating composition according to claim 63, wherein the surface of saidcoating thus rendered hydrophilic upon photoexcitation is operable topermit adherent moisture condensate and/or water droplets to spreadthereover to thereby prevent the substrate from being fogged or blurredwith adherent moisture condensate and/or water droplets.
 65. A coatingcomposition according to claim 63, wherein the surface of said coatingthus rendered hydrophilic upon photoexcitation is operable to permitadherent deposits and/or contaminants to be washed away by rainwater asthe substrate is subjected to rainfall whereby the surface isself-cleaned.
 66. A coating composition according to claim 63, whereinthe surface of said coating thus rendered hydrophilic uponphotoexcitation is operable to prevent contaminants from adhering to thesurface as contaminant-laden rainwater flows therealong.
 67. A coatingcomposition according to claim 63, wherein the surface of said coatingthus rendered hydrophilic upon photoexcitation is operable to releaseadherent deposits and/or contaminants when soaked in or wetted withwater to thereby facilitate cleansing of the substrate with water.
 68. Acoating composition according to claim 63, wherein the surface of saidcoating thus rendered hydrophilic upon photoexcitation is operable topermit adherent moisture condensate and/or water droplets to spreadthereover to thereby prevent growth of water droplets.
 69. A coatingcomposition according to claim 63, wherein the surface of said coatingthus rendered hydrophilic upon photoexcitation is operable to permitadherent moisture condensate and/or water droplets to spread thereoverto thereby promote drying of the substrate after wetted with water. 70.A composite with a hydrophilic surface, comprising: a substrate; and, aphotocatalytic layer bonded to the surface of said substrate andcomprised of a coating wherein particles of a photocatalyst areuniformly dispersed; said photocatalyst operating upon photoexcitationthereof to render the surface of said composite hydrophilic such thatthe surface of said composite presents a water wettability of less thanabout 5° in terms of the contact angle with water.
 71. An antifoggingtransparent sheet member comprising: a transparent substrate; and, asubstantially transparent photocatalytic layer bonded to the surface ofsaid substrate and comprised of a coating wherein particles of aphotocatalyst are uniformly dispersed; said photocatalyst operating uponphotoexcitation thereof to render the surface of said layer hydrophilicsuch that the surface of said layer presents a water wettability of lessthan about 5° in terms of the contact angle with water whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said layer to thereby prevent the substrate from being foggedor blurred with adherent moisture condensate and/or water droplets. 72.An antifogging mirror comprising: a substrate with a reflective coating;and, a substantially transparent photocatalytic layer bonded to thefront surface of said substrate and comprised of a coating whereinparticles of a photocatalyst are uniformly dispersed; said photocatalystoperating upon photoexcitation thereof to render the surface of saidlayer hydrophilic such that the surface of said layer presents a waterwettability of less than about 5° in terms of the contact angle withwater whereby adherent moisture condensate and/or water droplets arecaused to spread over the surface of said layer to thereby prevent thesubstrate from being fogged or blurred with adherent moisture condensateand/or water droplets.
 73. An antifogging lens comprising: a transparentlens-forming body; and, a substantially transparent photocatalytic layerbonded to the surface of said lens-forming body and comprised of acoating wherein particles of a photocatalyst are uniformly dispersed;said photocatalyst operating upon photoexcitation thereof to render thesurface of said layer hydrophilic such that the surface of said layerpresents a water wettability of less than about 5° in terms of thecontact angle with water whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of said layer tothereby prevent the lens-forming body from being fogged or blurred withadherent moisture condensate and/or water droplets.
 74. A composite witha hydrophilic surface, comprising: a substrate having a surface; and, aphotocatalytic layer bonded to the surface of said substrate andcomprised of a coating in which particles of a photocatalyst areuniformly dispersed; said photocatalyst operating upon photoexcitationthereof to render the surface of the composite hydrophilic wherebyadherent deposits and/or contaminants are washed away by rainwater toself-clean the composite as it is subjected to rainfall.
 75. A compositewith a hydrophilic surface, comprising: a substrate; and, aphotocatalytic layer bonded to the surface of said substrate andcomprised of a coating wherein particles of a photocatalyst areuniformly dispersed; said photocatalyst operating upon photoexcitationthereof to render the surface of the composite hydrophilic wherebycontaminants are prevented from adhering to the surface of the compositeas contaminant-laden rainwater flows therealong.
 76. A composite with ahydrophilic surface, comprising: a substrate; and, a photocatalyticlayer bonded to the surface of said substrate and comprised of a coatingwherein particles of a photocatalyst are uniformly dispersed; saidphotocatalyst operating upon photoexcitation thereof to render thesurface of the composite hydrophilic whereby deposits and/orcontaminants adhering to the surface are released therefrom when soakedin or wetted with water to thereby facilitate cleansing of the compositewith water.
 77. A composite with a hydrophilic surface, comprising: asubstrate; and, a photocatalytic layer bonded to the surface of saidsubstrate and comprised of a coating wherein particles of aphotocatalyst are uniformly dispersed; said photocatalyst operating uponphotoexcitation thereof to render the surface of the compositehydrophilic whereby adherent moisture condensate and/or water dropletsare caused to spread over the surface of said layer to thereby preventgrowth of water droplets.
 78. A composite with a hydrophilic surface,comprising: a substrate; and, a photocatalytic layer bonded to thesurface of said substrate and comprised of a coating wherein particlesof a photocatalyst are uniformly dispersed; said photocatalyst operatingupon photoexcitation thereof to render the surface of the compositehydrophilic whereby adherent water droplets are caused to spread overthe surface of said layer to thereby promote drying of the compositeafter wetted with water.
 79. A composite with a hydrophilic surface,comprising: a substrate; a photocatalytic layer bonded to the surface ofsaid substrate and comprised of a coating wherein particles of aphotocatalyst are uniformly dispersed; and, a hydrophilic protectivelayer covering said photocatalytic layer; said photocatalyst operatingupon photoexcitation thereof to render the surface of the compositehydrophilic.
 80. A composite with a hydrophilic surface, comprising: asubstrate; a photocatalytic layer bonded to the surface of saidsubstrate and comprised of a coating wherein particles of aphotocatalyst are uniformly dispersed; and, a protective layer coveringsaid photocatalytic layer, said protective layer being adapted to berendered hydrophilic upon photoexcitation; said photocatalyst operatingupon photoexcitation thereof to render the surface of the compositehydrophilic.
 81. A composite with a hydrophilic surface, comprising: asubstrate; and, a photocatalytic layer bonded to the surface of saidsubstrate and comprised of a coating wherein particles of aphotocatalyst are uniformly dispersed, said photocatalyst comprising anoxide selected from the group consisting of TiO₂, ZnO, SnO₂, SrTiO₃,WO₃, Bi₂O₃ and Fe₂O₃; said photocatalyst operating upon photoexcitationthereof to render the surface of the composite hydrophilic.
 82. Acomposite with a hydrophilic surface, comprising: a substrate; and, aphotocatalytic layer bonded to the surface of said substrate andcomprised of a coating wherein particles of a photocatalyst comprisingthe anatase form of titania are uniformly dispersed; said photocatalystoperating upon photoexcitation thereof to render the surface of thecomposite hydrophilic.
 83. A composite with a hydrophilic surface,comprising: a substrate; and, a photocatalytic layer bonded to thesurface of said substrate and comprised of a coating wherein particlesof a photocatalyst comprising the rutile form of titania are uniformlydispersed; said photocatalyst operating upon photoexcitation thereof torender the surface of the composite hydrophilic.
 84. A composite with ahydrophilic surface, comprising: a substrate; a photocatalytic layerbonded to the surface of said substrate and comprised of a coatingwherein particles of a photocatalyst comprising the rutile form oftitania are uniformly dispersed, said photocatalyst operating uponphotoexcitation thereof to render the surface of the compositehydrophilic; and, an intermediate layer of a non-decomposable materialinterleaved between said substrate and said photocatalytic layer.
 85. Acomposite with a hydrophilic surface, comprising: a substrate, saidsubstrate containing alkaline metal ions and/or alkaline-earth metalions; a photocatalytic layer bonded to the surface of said substrate andcomprised of a coating wherein particles of a photocatalyst comprisingthe rutile form of titania are uniformly dispersed, said photocatalystoperating upon photoexcitation thereof to render the surface of thecomposite hydrophilic; and, a diffusion prevention thin film interleavedbetween said substrate and said photocatalytic layer to prevent saidions from diffusing from said substrate into said photocatalytic layer.86. A composite according to claim 85, wherein said thin film iscomprised of silica.
 87. A composite with a hydrophilic surface,comprising: a substrate; and, a photocatalytic layer bonded to thesurface of said substrate and comprised of a coating wherein particlesof a photocatalyst are uniformly dispersed; said photocatalytic layerhaving a thickness of less than about 0.2 micrometers; saidphotocatalyst operating upon photoexcitation thereof to render thesurface of the composite hydrophilic.
 88. A composite with a hydrophilicsurface, comprising: a substrate; and, a photocatalytic layer bonded tothe surface of said substrate and comprised of a coating whereinparticles of a photocatalyst are uniformly dispersed; saidphotocatalytic layer further comprising a metal selected from the groupconsisting of Ag, Cu and Zn; said photocatalyst operating uponphotoexcitation thereof to render the surface of the compositehydrophilic.
 89. A composite with a hydrophilic surface, comprising: asubstrate; and, a photocatalytic layer bonded to the surface of saidsubstrate and comprised of a coating wherein particles of aphotocatalyst are uniformly dispersed; said photocatalytic layer furthercomprising a metal selected from the group consisting of Pt, Pd, Rh, Ru,Os and Ir; said photocatalyst operating upon photoexcitation thereof torender the surface of the composite hydrophilic.
 90. A composite with ahydrophilic surface, comprising: a substrate; and, a photocatalyticlayer bonded to the surface of said substrate and comprised of a coatingwherein particles of a photocatalyst are uniformly dispersed; saidphotocatalyst operating upon photoexcitation thereof to render thesurface of said composite hydrophilic such that the surface of saidcomposite presents a water wettability of less than about 10° in termsof the contact angle with water.
 91. A composite according to claim 90,wherein upon photoexcitation the surface of said composite presents awater wettability of less than about 5° in terms of the contact anglewith water.
 92. A composite with a hydrophilic surface, comprising: asubstrate having a surface; and, a photocatalytic layer bonded to thesurface of said substrate, said photocatalytic layer comprising aphotocatalyst and SiO₂ or SnO₂; said photocatalyst operating uponphotoexcitation thereof to render the surface of the compositehydrophilic.
 93. An antifogging transparent sheet member comprising: atransparent substrate; and, a substantially transparent photocatalyticlayer bonded to the surface of said substrate and comprised of aphotocatalyst and SiO₂ or SnO₂; said photocatalyst operating uponphotoexcitation thereof to render the surface of said layer hydrophilicwhereby adherent moisture condensate and/or water droplets are caused tospread over the surface of said layer to thereby prevent the substratefrom being fogged or blurred with adherent moisture condensate and/orwater droplets.
 94. An antifogging mirror comprising: a substrate with areflective coating; and, a substantially transparent photocatalyticlayer bonded to the front surface of said substrate and comprised of aphotocatalyst and SiO₂ or SnO₂; said photocatalyst operating uponphotoexcitation thereof to render the surface of said layer hydrophilicwhereby adherent moisture condensate and/or water droplets are caused tospread over the surface of said layer to thereby prevent the substratefrom being fogged or blurred with adherent moisture condensate and/orwater droplets.
 95. An antifogging lens comprising: a transparentlens-forming body; and, a substantially transparent photocatalytic layerbonded to the surface of said lens-forming body and comprised of aphotocatalyst and SiO₂ or SnO₂; said photocatalyst operating uponphotoexcitation thereof to render the surface of said layer hydrophilicwhereby adherent moisture condensate and/or water droplets are caused tospread over the surface of said layer to thereby prevent thelens-forming body from being fogged or blurred with adherent moisturecondensate and/or water droplets.
 96. A composite with a hydrophilicsurface, comprising: a substrate; and, a photocatalytic layer bonded tothe surface of said substrate and comprised of a photocatalyst and SiO₂or SnO₂; said photocatalyst operating upon photoexcitation thereof torender the surface of the composite hydrophilic whereby adherentdeposits and/or contaminants are washed away by rainwater to self-cleanthe composite as it is subjected to rainfall.
 97. A composite with ahydrophilic surface, comprising: a substrate; and, a photocatalyticlayer bonded to the surface of said substrate and comprised of aphotocatalyst and SiO₂ or SnO₂; said photocatalyst operating uponphotoexcitation thereof to render the surface of the compositehydrophilic whereby contaminants are prevented from adhering to thesurface of the composite as contaminant-laden rainwater flowstherealong.
 98. A composite with a hydrophilic surface, comprising: asubstrate; and, a photocatalytic layer bonded to the surface of saidsubstrate and comprised of a photocatalyst and SiO₂ or SnO₂; saidphotocatalyst operating upon photoexcitation thereof to render thesurface of the composite hydrophilic whereby deposits and/orcontaminants adhering to the surface are released therefrom when soakedin or wetted with water to thereby facilitate cleansing of the compositewith water.
 99. A composite with a hydrophilic surface, comprising: asubstrate; and, a photocatalytic layer bonded to the surface of saidsubstrate and comprised of a photocatalyst and SiO₂ or SnO₂; saidphotocatalyst operating upon photoexcitation thereof to render thesurface of the composite hydrophilic whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer to thereby prevent growth of water droplets.
 100. Acomposite with a hydrophilic surface, comprising: a substrate; and, aphotocatalytic layer bonded to the surface of said substrate andcomprised of a photocatalyst and SiO₂ or SnO₂; said photocatalystoperating upon photoexcitation thereof to render the surface of thecomposite hydrophilic whereby adherent water droplets are caused tospread over the surface of said layer to thereby promote drying of thecomposite after wetted with water.
 101. A composite according to one ofclaims 92-100, wherein upon photoexcitation the surface of saidcomposite presents a water wettability of less than about 10° in termsof the contact angle with water.
 102. A composite according to claim101, wherein upon photoexcitation the surface of said composite presentsa water wettability of less than about 5° in terms of the contact anglewith water.
 103. A composite with a hydrophilic surface, comprising: asubstrate having a surface; and, a photocatalytic coating bonded to thesurface of said substrate and comprised of a photocatalyst and siliconehaving organic groups bonded to silicon atoms of silicone molecules;wherein due to photoexcitation of said photocatalyst said organic groupat the surface of said photocatalytic coating are substituted at leastin part with hydroxyl groups under the photocatalytic action of thephotocatalyst thereby rendering the surface of the compositehydrophilic.
 104. An antifogging transparent sheet member comprising: atransparent substrate having a surface; and, a substantially transparentphotocatalytic coating bonded to the surface of said substrate andcomprised of a photocatalyst and silicone having organic groups bondedto silicon atoms of silicone molecules; wherein due to photoexcitationof said photocatalyst said organic group at the surface of saidphotocatalytic coating are substituted at least in part with hydroxylgroups under the photocatalytic action of the photocatalyst therebyrendering the surface of the sheet member hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said coating to thereby prevent the substrate from beingfogged or blurred with adherent moisture condensate and/or waterdroplets.
 105. An antifogging mirror comprising: a substrate having asurface and a reflective coating; and, a substantially transparentphotocatalytic coating bonded to the surface of said substrate andcomprised of a photocatalyst and silicone having organic groups bondedto silicon atoms of silicone molecules; wherein due to photoexcitationof said photocatalyst said organic group at the surface of saidphotocatalytic coating are substituted at least in part with hydroxylgroups under the photocatalytic action of the photocatalyst therebyrendering the surface of the mirror hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said coating to thereby prevent the substrate from beingfogged or blurred with adherent moisture condensate and/or waterdroplets.
 106. An antifogging lens comprising: a transparentlens-forming body having a surface; and, a substantially transparentphotocatalytic coating bonded to the surface of said lens-forming bodyand comprised of a photocatalyst and silicone having organic groupsbonded to silicon atoms of silicone molecules; wherein due tophotoexcitation of said photocatalyst said organic group at the surfaceof said photocatalytic coating are substituted at least in part withhydroxyl groups under the photocatalytic action of the photocatalystthereby rendering the surface of the lens hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said coating to thereby prevent the body from being fogged orblurred with adherent moisture condensate and/or water droplets.
 107. Acomposite with a hydrophilic surface, comprising: a substrate having asurface; and, a photocatalytic coating bonded to the surface of saidsubstrate and comprised of a photocatalyst and silicone having organicgroups bonded to silicon atoms of silicone molecules; wherein due tophotoexcitation of said photocatalyst said organic group at the surfaceof said photocatalytic coating are substituted at least in part withhydroxyl groups under the photocatalytic action of the photocatalystthereby rendering the surface of the composite hydrophilic wherebyadherent deposits and/or contaminants are washed away by rainwater toself-clean the composite as it is subjected to rainfall.
 108. Acomposite with a hydrophilic surface, comprising: a substrate having asurface; and, a photocatalytic coating bonded to the surface of saidsubstrate and comprised of a photocatalyst and silicone having organicgroups bonded to silicon atoms of silicone molecules; wherein due tophotoexcitation of said photocatalyst said organic group at the surfaceof said photocatalytic coating are substituted at least in part withhydroxyl groups under the photocatalytic action of the photocatalystthereby rendering the surface of the composite hydrophilic wherebycontaminants are prevented from adhering to the surface of the compositeas contaminant-laden rainwater flows therealong.
 109. A composite with ahydrophilic surface, comprising: a substrate having a surface; and, aphotocatalytic coating bonded to the surface of said substrate andcomprised of a photocatalyst and silicone having organic groups bondedto silicon atoms of silicone molecules; wherein due to photoexcitationof said photocatalyst said organic group at the surface of saidphotocatalytic coating are substituted at least in part with hydroxylgroups under the photocatalytic action of the photocatalyst therebyrendering the surface of the composite hydrophilic whereby depositsand/or contaminants adhering to the surface are released therefrom whensoaked in or wetted with water to thereby facilitate cleansing of thecomposite with water.
 110. A composite with a hydrophilic surface,comprising: a substrate having a surface; and, a photocatalytic coatingbonded to the surface of said substrate and comprised of a photocatalystand silicone having organic groups bonded to silicon atoms of siliconemolecules; wherein due to photoexcitation of said photocatalyst saidorganic group at the surface of said photocatalytic coating aresubstituted at least in part with hydroxyl groups under thephotocatalytic action of the photocatalyst thereby rendering the surfaceof the composite hydrophilic whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of the coating tothereby prevent growth of water droplets.
 111. A composite with ahydrophilic surface, comprising: a substrate having a surface; and, aphotocatalytic coating bonded to the surface of said substrate andcomprised of a photocatalyst and silicone having organic groups bondedto silicon atoms of silicone molecules; wherein due to photoexcitationof said photocatalyst said organic group at the surface of saidphotocatalytic coating are substituted at least in part with hydroxylgroups under the photocatalytic action of the photocatalyst therebyrendering the surface of the composite hydrophilic whereby adherentwater droplets are caused to spread over the surface of the coating tothereby promote drying of the composite after wetted with water.
 112. Acomposite according to one of claims 103-111, wherein uponphotoexcitation the surface of said composite presents a waterwettability of less than about 10° in terms of the contact angle withwater.
 113. A composite according to claim 112, wherein uponphotoexcitation the surface of said composite presents a waterwettability of less than about 5° in terms of the contact angle withwater.
 114. An antifogging sheet glass adapted to prevent moisturecondensate and/or water droplets adhering on the surface thereof fromfogging or blurring the sheet glass, said sheet glass comprising: atransparent substrate having a surface; and, a substantially transparentcoating of silicone which is bonded to the surface of said substrate andin which particles of a photocatalyst are uniformly dispersed, saidsilicone having organic groups bonded to silicon atoms of siliconemolecules; wherein said organic groups at the surface of said coatingare capable of being substituted, upon photoexcitation of saidphotocatalyst, at least in part with hydroxyl groups whereby the surfaceof said substrate is rendered highly hydrophilic.
 115. An antifoggingmirror adapted to prevent moisture condensate and/or water dropletsadhering on the surface thereof from fogging or blurring the mirror,said mirror comprising: a substrate having a surface and a reflectivecoating; and, a substantially transparent coating of silicone which isbonded to the surface of said substrate and in which particles of aphotocatalyst are uniformly dispersed, said silicone having organicgroups bonded to silicon atoms of silicone molecules; wherein saidorganic groups at the surface of said coating are capable of beingsubstituted, upon photoexcitation of said photocatalyst, at least inpart with hydroxyl groups whereby the surface of said substrate isrendered highly hydrophilic.
 116. An antifogging lens adapted to preventmoisture condensate and/or water droplets adhering on the surfacethereof from fogging or blurring the lens, said lens comprising: atransparent lens-forming body having a surface; and, a substantiallytransparent coating of silicone which is bonded to the surface of saidbody and in which particles of a photocatalyst are uniformly dispersed,said silicone having organic groups bonded to silicon atoms of siliconemolecules; wherein said organic groups at the surface of said coatingare capable of being substituted, upon photoexcitation of saidphotocatalyst, at least in part with hydroxyl groups whereby the surfaceof said substrate is rendered highly hydrophilic.
 117. A composite witha hydrophilifiable surface, comprising: a substrate having a surface;and, a photocatalytic coating bonded to the surface of said substrateand comprised of a photocatalyst and silicone having organic groupsbonded to silicon atoms of silicone molecules; wherein said organicgroups at the surface of said coating are capable of being substituted,upon photoexcitation of said photocatalyst, at least in part withhydroxyl groups to render the surface of said composite hydrophilic suchthat the surface of said composite presents a water wettability of lessthan about 10° in terms of the contact angle with water.
 118. Acomposite with a hydrophilifiable surface, comprising: a substratehaving a surface; and, a photocatalytic coating bonded to the surface ofsaid substrate and comprised of a photocatalyst and silicone havingorganic groups bonded to silicon atoms of silicone molecules; whereinsaid organic groups at the surface of said coating are capable of beingsubstituted, upon photoexcitation of said photocatalyst, at least inpart with hydroxyl groups to render the surface of said compositehydrophilic such that the surface of said composite presents a waterwettability of less than about 10° in terms of the contact angle withwater whereby adherent deposits and/or contaminants are washed away byrainwater to self-clean the composite as it is subjected to rainfall.119. A composite with a hydrophilifiable surface, comprising: asubstrate having a surface; and, a photocatalytic coating bonded to thesurface of said substrate and comprised of a photocatalyst and siliconehaving organic groups bonded to silicon atoms of silicone molecules;wherein said organic groups at the surface of said coating are capableof being substituted, upon photoexcitation of said photocatalyst, atleast in part with hydroxyl groups to render the surface of saidcomposite hydrophilic such that the surface of said composite presents awater wettability of less than about 10° in terms of the contact anglewith water whereby contaminants are prevented from adhering to thesurface of the composite as contaminant-laden rainwater flowstherealong.
 120. A composite with a hydrophilifiable surface,comprising: a substrate having a surface; and, a photocatalytic coatingbonded to the surface of said substrate and comprised of a photocatalystand silicone having organic groups bonded to silicon atoms of siliconemolecules; wherein said organic groups at the surface of said coatingare capable of being substituted, upon photoexcitation of saidphotocatalyst, at least in part with hydroxyl groups to render thesurface of said composite hydrophilic such that the surface of saidcomposite presents a water wettability of less than about 10° in termsof the contact angle with water whereby deposits and/or contaminantsadhering to the surface are released therefrom when soaked in or wettedwith water to thereby facilitate cleansing of the composite with water.121. A composite with a hydrophilifiable surface, comprising: asubstrate having a surface; and, a photocatalytic coating bonded to thesurface of said substrate and comprised of a photocatalyst and siliconehaving organic groups bonded to silicon atoms of silicone molecules;wherein said organic groups at the surface of said coating are capableof being substituted, upon photoexcitation of said photocatalyst, atleast in part with hydroxyl groups to render the surface of saidcomposite hydrophilic such that the surface of said composite presents awater wettability of less than about 10° in terms of the contact anglewith water whereby adherent moisture condensate and/or water dropletsare caused to spread over the surface of the coating to thereby preventgrowth of water droplets.
 122. A composite with a hydrophilifiablesurface, comprising: a substrate having a surface; and, a photocatalyticcoating bonded to the surface of said substrate and comprised of aphotocatalyst and silicone having organic groups bonded to silicon atomsof silicone molecules; wherein said organic groups at the surface ofsaid coating are capable of being substituted, upon photoexcitation ofsaid photocatalyst, at least in part with hydroxyl groups to render thesurface of said composite hydrophilic such that the surface of saidcomposite presents a water wettability of less than about 10° in termsof the contact angle with water whereby adherent water droplets arecaused to spread over the surface of the coating to thereby promotedrying of the composite after wetted with water.
 123. A method ofmanufacturing a composite with a hydrophilifiable surface, comprisingthe steps of: preparing a substrate having a surface; applying onto thesurface of the substrate a suspension comprising crystalline titaniaparticles dispersed in a precursor of amorphous silica; and, subjectingsaid precursor to hydrolysis where necessary and to dehydrationpolymerization to thereby form on said surface a photo-reactive layer oftitania particles bound by amorphous silica.
 124. A method ofmanufacturing an antifogging transparent sheet member, comprising thesteps of: preparing a transparent substrate having a surface; applyingonto the surface of the substrate a suspension comprising crystallinetitania particles dispersed in a precursor of amorphous silica; and,subjecting said precursor to hydrolysis where necessary and todehydration polymerization to thereby form on said surface asubstantially transparent photo-reactive layer of titania particlesbound by amorphous silica.
 125. A method of manufacturing aself-cleaning composite, comprising the steps of: preparing a substratehaving a surface; applying onto the surface of the substrate asuspension comprising crystalline titania particles dispersed in aprecursor of amorphous silica; and, subjecting said precursor tohydrolysis where necessary and to dehydration polymerization to therebyform on said surface a photo-reactive layer of titania particles boundby amorphous silica.
 126. A method of manufacturing an antifoggingmirror, comprising the steps of: preparing a substrate with or without areflective coating, said substrate having a surface; applying onto thesurface of the substrate a suspension comprising crystalline titaniaparticles dispersed in a precursor of amorphous silica; subjecting saidprecursor to hydrolysis where necessary and to dehydrationpolymerization to thereby form on said surface a substantiallytransparent photo-reactive layer of titania particles bound by amorphoussilica; and, forming where necessary a reflective coating on theopposite surface of said substrate prior to or subsequent to or duringthe course of said step of applying a suspension.
 127. A method ofmanufacturing an antifogging lens, comprising the steps of: preparing alens-forming body having a surface; applying onto the surface of thesubstrate a suspension comprising crystalline titania particlesdispersed in a precursor of amorphous silica; and, subjecting saidprecursor to hydrolysis where necessary and to dehydrationpolymerization to thereby form on said surface a substantiallytransparent photo-reactive layer of titania particles bound by amorphoussilica.
 128. A method according to one of claims 123-127, wherein saidprecursor is tetraalkoxysilane, silanol, polysiloxane having an averagemolecular weight of less than 3000, or a mixture thereof.
 129. A methodof manufacturing a composite with a hydrophilifiable surface, comprisingthe steps of: preparing a substrate having a surface; applying onto thesurface of the substrate a suspension comprising particles of silicadispersed in a solution of an organic compound of titanium; subjectingsaid compound to hydrolysis and dehydration polymerization to form athin film of amorphous titania in which particles of silica aredispersed; and, heating said film at a temperature less than thesoftening point of the substrate to transform amorphous titania intocrystalline titania to thereby form a photo-reactive coating ofphotocatalytic titania in which particles of silica are dispersed. 130.A method of manufacturing an antifogging transparent sheet member,comprising the steps of: preparing a transparent substrate having asurface; applying onto the surface of the substrate a suspensioncomprising particles of silica dispersed in a solution of an organiccompound of titanium; subjecting said compound to hydrolysis anddehydration polymerization to form a thin film of amorphous titania inwhich particles of silica are dispersed; and, heating said film at atemperature less than the softening point of the substrate to transformamorphous titania into crystalline titania to thereby form asubstantially transparent photo-reactive coating of photocatalytictitania in which particles of silica are dispersed.
 131. A method ofmanufacturing a self-cleaning composite, comprising the steps of:preparing a substrate having a surface; applying onto the surface of thesubstrate a suspension comprising particles of silica dispersed in asolution of an organic compound of titanium; subjecting said compound tohydrolysis and dehydration polymerization to form a thin film ofamorphous titania in which particles of silica are dispersed; and,heating said film at a temperature less than the softening point of thesubstrate to transform amorphous titania into crystalline titania tothereby form a photo-reactive coating of photocatalytic titania in whichparticles of silica are dispersed.
 132. A method of manufacturing anantifogging mirror, comprising the steps of: preparing a substrate withor without a reflective coating, said substrate having a surface;applying onto the surface of the substrate a suspension comprisingparticles of silica dispersed in a solution of an organic compound oftitanium; subjecting said compound to hydrolysis and dehydrationpolymerization to form a thin film of amorphous titania in whichparticles of silica are dispersed; heating said film at a temperatureless than the softening point of the substrate to transform amorphoustitania into crystalline titania to thereby form a substantiallytransparent photo-reactive coating of photocatalytic titania in whichparticles of silica are dispersed; and, forming where necessary areflective coating on the opposite surface of said substrate prior to orsubsequent to or during the course of said step of applying asuspension.
 133. A method of manufacturing an antifogging lens,comprising the steps of: preparing a lens-forming body having a surface;applying onto the surface of the body a suspension comprising particlesof silica dispersed in a solution of an organic compound of titanium;subjecting said compound to hydrolysis and dehydration polymerization toform a thin film of amorphous titania in which particles of silica aredispersed; and, heating said film at a temperature less than thesoftening point of the body to transform amorphous titania intocrystalline titania to thereby form a substantially transparentphoto-reactive coating of photocatalytic titania in which particles ofsilica are dispersed.
 134. A method according to one of claims 129-133,wherein said organic compound of titanium is selected from the groupconsisting of an alkoxide of titanium, a chelate of titanium and anacetate of titanium.
 135. A method of manufacturing a composite with ahydrophilifiable surface, comprising the steps of: preparing a substratehaving a surface; applying onto the surface of the substrate asuspension comprising particles of crystalline titania and particles ofsilica; and, heating said substrate at a temperature less than thesoftening point thereof to bond particles to said substrate and tosinter particles with each other to thereby form a photo-reactivecoating comprised of sintered particles of titania and silica.
 136. Amethod of manufacturing an antifogging transparent sheet member,comprising the steps of: preparing a transparent substrate having asurface; applying onto the surface of the substrate a suspensioncomprising particles of crystalline titania and particles of silica;and, heating said substrate at a temperature less than the softeningpoint thereof to bond particles to said substrate and to sinterparticles with each other to thereby form a substantially transparentphoto-reactive coating comprised of sintered particles of titania andsilica.
 137. A method of manufacturing a self-cleaning composite,comprising the steps of: preparing a substrate having a surface;applying onto the surface of the substrate a suspension comprisingparticles of crystalline titania and particles of silica; and, heatingsaid substrate at a temperature less than the softening point thereof tobond particles to said substrate and to sinter particles with each otherto thereby form a photo-reactive coating comprised of sintered particlesof titania and silica.
 138. A method of manufacturing an antifoggingmirror, comprising the steps of: preparing a substrate with or without areflective coating, said substrate having a surface; applying onto thesurface of the substrate a suspension comprising particles ofcrystalline titania and particles of silica; heating said substrate at atemperature less than the softening point thereof to bond particles tosaid substrate and to sinter particles with each other to thereby form asubstantially transparent photo-reactive coating comprised of sinteredparticles of titania and silica; and, forming where necessary areflective coating on the opposite surface of said substrate prior to orsubsequent to or during the course of said step of applying asuspension.
 139. A method of manufacturing an antifogging lens,comprising the steps of: preparing a lens-forming body having a surface;applying onto the surface of the body a suspension comprising particlesof crystalline titania and particles of silica; and, heating said bodyat a temperature less than the softening point thereof to bond particlesto said substrate and to sinter particles with each other to therebyform a substantially transparent photo-reactive coating comprised ofsintered particles of titania and silica.
 140. A method of manufacturinga composite with a hydrophilifiable surface, comprising the steps of:preparing a substrate having a surface; applying onto the surface of thesubstrate a suspension comprising particles of the anatase form oftitania and particles of tin oxide; and, heating said substrate at atemperature of less than 900° C. to bond particles to said substrate andto sinter particles with each other to thereby form a photo-reactivecoating comprised of sintered particles of titania and tin oxide.
 141. Amethod of manufacturing an antifogging transparent sheet member,comprising the steps of: preparing a transparent substrate having asurface; applying onto the surface of the substrate a suspensioncomprising particles of the anatase form of titania and particles of tinoxide; and, heating said substrate at a temperature of less than 900° C.to bond particles to said substrate and to sinter particles with eachother to thereby form a substantially transparent photo-reactive coatingcomprised of sintered particles of titania and tin oxide.
 142. A methodof manufacturing a self-cleaning composite, comprising the steps of:preparing a substrate having a surface; applying onto the surface of thesubstrate a suspension comprising particles of the anatase form oftitania and particles of tin oxide; and, heating said substrate at atemperature of less than 900° C. to bond particles to said substrate andto sinter particles with each other to thereby form a photo-reactivecoating comprised of sintered particles of titania and tin oxide.
 143. Amethod of manufacturing an antifogging mirror, comprising the steps of:preparing a substrate with or without a reflective coating, saidsubstrate having a surface; applying onto the surface of the substrate asuspension comprising particles of the anatase form of titania andparticles of tin oxide; heating said substrate at a temperature of lessthan 900° C. to bond particles to said substrate and to sinter particleswith each other to thereby form a substantially transparentphoto-reactive coating comprised of sintered particles of titania andtin oxide; and, forming where necessary a reflective coating on theopposite surface of said substrate prior to or subsequent to or duringthe course of said step of applying a suspension.
 144. A method ofmanufacturing an antifogging lens, comprising the steps of: preparing alens-forming body having a surface; applying onto the surface of thesubstrate a suspension comprising particles of the anatase form oftitania and particles of tin oxide; heating said body at a temperatureof less than 900° C. to bond particles to said substrate and to sinterparticles with each other to thereby form a substantially transparentphoto-reactive coating comprised of sintered particles of titania andtin oxide.
 145. A method of manufacturing a composite with ahydrophilifiable surface, comprising the steps of: preparing a substratehaving a surface; applying onto the surface of the substrate asuspension comprising particles of tin oxide dispersed in a solution ofan organic compound of titanium; subjecting said compound to hydrolysisand dehydration polymerization to thereby form a thin film of amorphoustitania in which particles of tin oxide are dispersed; and, heating saidthin film at a temperature of less than 900° C. to transform amorphoustitania into crystalline titania to thereby form a photo-reactivecoating of photocatalytic titania in which particles of tin oxide aredispersed.
 146. A method of manufacturing an antifogging transparentsheet member, comprising the steps of: preparing a transparent substratehaving a surface; applying onto the surface of the substrate asuspension comprising particles of tin oxide dispersed in a solution ofan organic compound of titanium; subjecting said compound to hydrolysisand dehydration polymerization to thereby form a thin film of amorphoustitania in which particles of tin oxide are dispersed; and, heating saidthin film at a temperature of less than 900° C. to transform amorphoustitania into crystalline titania to thereby form a substantiallytransparent photo-reactive coating of photocatalytic titania in whichparticles of tin oxide are dispersed.
 147. A method of manufacturing aself-cleaning composite, comprising the steps of: preparing a substratehaving a surface; applying onto the surface of the substrate asuspension comprising particles of tin oxide dispersed in a solution ofan organic compound of titanium; subjecting said compound to hydrolysisand dehydration polymerization to thereby form a thin film of amorphoustitania in which particles of tin oxide are dispersed; and, heating saidthin film at a temperature of less than 900° C. to transform amorphoustitania into crystalline titania to thereby form a photo-reactivecoating of photocatalytic titania in which particles of tin oxide aredispersed.
 148. A method of manufacturing an antifogging mirror,comprising the steps of: preparing a substrate with or without areflective coating, said substrate having a surface; applying onto thesurface of the substrate a suspension comprising particles of tin oxidedispersed in a solution of an organic compound of titanium; subjectingsaid compound to hydrolysis and dehydration polymerization to therebyform a thin film of amorphous titania in which particles of tin oxideare dispersed; heating said thin film at a temperature of less than 900°C. to transform amorphous titania into crystalline titania to therebyform a substantially transparent photo-reactive coating ofphotocatalytic titania in which particles of tin oxide are dispersed;and, forming where necessary a reflective coating on the oppositesurface of said substrate prior to or subsequent to or during the courseof said step of applying a suspension.
 149. A method of manufacturing anantifogging lens, comprising the steps of: preparing a lens-forming bodyhaving a surface; applying onto the surface of the body a suspensioncomprising particles of tin oxide dispersed in a solution of an organiccompound of titanium; subjecting said compound to hydrolysis anddehydration polymerization to thereby form a thin film of amorphoustitania in which particles of tin oxide are dispersed; and, heating saidthin film at a temperature of less than 900° C. to transform amorphoustitania into crystalline titania to thereby form a substantiallytransparent photo-reactive coating of photocatalytic titania in whichparticles of tin oxide are dispersed.
 150. A method of manufacturing acomposite with a hydrophilic surface, comprising the steps of: preparinga substrate having a surface; applying onto the surface of the substratea coating composition comprising particles of a photocatalyst and afilm-forming element of uncured or partially cured silicone or aprecursor thereof; curing said film-forming element to form a siliconecoating in which particles of the photocatalyst are uniformly dispersed,said silicone coating having organic groups bonded to silicon atoms ofsilicone molecules; and, subjecting the photocatalyst to photoexcitationso that said organic groups at the surface of the coating aresubstituted at least in part with hydroxyl groups.
 151. A method ofmanufacturing an antifogging transparent sheet member, comprising thesteps of: preparing a transparent substrate having a surface; applyingonto the surface of the substrate a coating composition comprisingparticles of a photocatalyst and a film-forming element of uncured orpartially cured silicone or a precursor thereof; curing saidfilm-forming element to form a substantially transparent siliconecoating in which particles of the photocatalyst are uniformly dispersed,said silicone coating having organic groups bonded to silicon atoms ofsilicone molecules; and, subjecting the photocatalyst to photoexcitationso that said organic groups at the surface of the coating aresubstituted at least in part with hydroxyl groups.
 152. A method ofmanufacturing a self-cleaning composite, comprising the steps of:preparing a substrate having a surface; applying onto the surface of thesubstrate a coating composition comprising particles of a photocatalystand a film-forming element of uncured or partially cured silicone or aprecursor thereof; curing said film-forming element to form a siliconecoating in which particles of the photocatalyst are uniformly dispersed,said silicone coating having organic groups bonded to silicon atoms ofsilicone molecules; and, subjecting the photocatalyst to photoexcitationso that said organic groups at the surface of the coating aresubstituted at least in part with hydroxyl groups.
 153. A method ofmanufacturing an antifogging mirror, comprising the steps of: preparinga substrate with or without a reflective coating, said substrate havinga surface; applying onto the surface of the substrate a coatingcomposition comprising particles of a photocatalyst and a film-formingelement of uncured or partially cured silicone or a precursor thereof;curing said film-forming element to form a substantially transparentsilicone coating in which particles of the photocatalyst are uniformlydispersed, said silicone coating having organic groups bonded to siliconatoms of silicone molecules; subjecting the photocatalyst tophotoexcitation so that said organic groups at the surface of thecoating are substituted at least in part with hydroxyl groups; and,forming where necessary a reflective coating on the opposite surface ofsaid substrate prior to or subsequent to or during the course of saidstep of applying a coating composition.
 154. A method of manufacturingan antifogging lens, comprising the steps of: preparing a lens-formingbody having a surface; applying onto the surface of the body a coatingcomposition comprising particles of a photocatalyst and a film-formingelement of uncured or partially cured silicone or a precursor thereof;curing said film-forming element to form a substantially transparentsilicone coating in which particles of the photocatalyst are uniformlydispersed, said silicone coating having organic groups bonded to siliconatoms of silicone molecules; and, subjecting the photocatalyst tophotoexcitation so that said organic groups at the surface of thecoating are substituted at least in part with hydroxyl groups.
 155. Amethod according to one of claims 150-154, wherein said step ofsubjecting the photocatalyst to photoexcitation is carried out until thewater wettability of the surface of said coating becomes less than about10° in terms of the contact angle with water.
 156. A method according toclaim 155, wherein said step of subjecting the photocatalyst tophotoexcitation is carried out until the water wettability of thesurface of said coating becomes less than about 5° in terms of thecontact angle with water.
 157. A coating composition for use in forminga photocatalytically hydrophilifiable coating on a substrate, saidcoating composition comprising: a film-forming element comprising aprecursor of amorphous silica and capable of forming a coating ofamorphous silica when cured; and, particles of photocatalytic titaniadispersed in said film-forming element for rendering uponphotoexcitation the surface of said coating hydrophilic on the order ofless than about 10° in terms of the contact angle with water.
 158. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoussilica and capable of forming a coating of amorphous silica when cured;and, particles of photocatalytic titania dispersed in said film-formingelement for rendering upon photoexcitation the surface of said coatinghydrophilic; said coating having the surface thus rendered hydrophilicbeing operable to permit adherent moisture condensate and/or waterdroplets to spread thereover to thereby prevent the substrate from beingfogged or blurred with adherent moisture condensate and/or waterdroplets.
 159. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous silica and capable of forming a coating of amorphous silicawhen cured; and, particles of photocatalytic titania dispersed in saidfilm-forming element for rendering upon photoexcitation the surface ofsaid coating hydrophilic; said coating having the surface thus renderedhydrophilic being operable to permit adherent deposits and/orcontaminants to be washed away by rainwater as said substrate issubjected to rainfall to thereby permit self-cleaning of the substrate.160. A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoussilica and capable of forming a coating of amorphous silica when cured;and, particles of photocatalytic titania dispersed in said film-formingelement for rendering upon photoexcitation the surface of said coatinghydrophilic; said coating having the surface thus rendered hydrophilicbeing operable to prevent contaminants from adhering to the surfacethereof as contaminant-laden rainwater flows therealong.
 161. A coatingcomposition for use in forming a photocatalytically hydrophilifiablecoating on a substrate, said coating composition comprising: afilm-forming element comprising a precursor of amorphous silica andcapable of forming a coating of amorphous silica when cured; and,particles of photocatalytic titania dispersed in said film-formingelement for rendering upon photoexcitation the surface of said coatinghydrophilic; said coating having the surface thus rendered hydrophilicbeing operable to release adherent deposits and/or contaminants whensoaked in or wetted with water to thereby facilitate cleansing of thesubstrate with water.
 162. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous silica and capable of forming a coating of amorphous silicawhen cured; and, particles of photocatalytic titania dispersed in saidfilm-forming element for rendering upon photoexcitation the surface ofsaid coating hydrophilic; said coating having the surface thus renderedhydrophilic being operable to cause adherent moisture condensate and/orwater droplets to spread over the surface of the coating to therebyprevent growth of water droplets.
 163. A coating composition for use informing a photocatalytically hydrophilifiable coating on a substrate,said coating composition comprising: a film-forming element comprising aprecursor of amorphous silica and capable of forming a coating ofamorphous silica when cured; and, particles of photocatalytic titaniadispersed in said film-forming element for rendering uponphotoexcitation the surface of said coating hydrophilic; said coatinghaving the surface thus rendered hydrophilic being operable to causeadherent water droplets to spread over the surface of the coating tothereby promote drying of the substrate after wetted with water.
 164. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoussilica and capable of forming a coating of amorphous silica when cured,said precursor being tetraalkoxysilane, silanol, polysiloxane having anaverage molecular weight of less than 3000, or a mixture thereof; and,particles of photocatalytic titania dispersed in said film-formingelement for rendering upon photoexcitation the surface of said coatinghydrophilic.
 165. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous titania and capable of forming a coating of photocatalytictitania upon curing and calcination; and, particles of silica dispersedin said film-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic on the order ofless than about 10° in terms of the contact angle with water.
 166. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of silica dispersed in saidfilm-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said coating to thereby prevent the substrate from beingfogged or blurred with adherent moisture condensate and/or waterdroplets.
 167. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous titania and capable of forming a coating of photocatalytictitania upon curing and calcination; and, particles of silica dispersedin said film-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentdeposits and/or contaminants are away by rainwater as said substrate issubjected to rainfall to thereby permit self-cleaning of the substrate.168. A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of silica dispersed in saidfilm-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic wherebycontaminants are prevented from adhering to the surface of the substrateas contaminant-laden rainwater flows therealong.
 169. A coatingcomposition for use in forming a photocatalytically hydrophilifiablecoating on a substrate, said coating composition comprising: afilm-forming element comprising a precursor of amorphous titania andcapable of forming a coating of photocatalytic titania upon curing andcalcination; and, particles of silica dispersed in said film-formingelement; said photocatalytic titania rendering upon photoexcitation thesurface of said coating hydrophilic whereby deposits and/or contaminantsadhering to the surface are released therefrom when soaked in or wettedwith water to thereby facilitate cleansing of the substrate with water.170. A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of silica dispersed in saidfilm-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of the coating to thereby prevent growth of water droplets. 171.A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of silica dispersed in saidfilm-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentwater droplets are caused to spread over the surface of the coating tothereby promote drying of the substrate after wetted with water.
 172. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination, said precursor being selected from the groupconsisting of an alkoxide of titanium, a chelate of titanium and anacetate of titanium; and, particles of silica dispersed in saidfilm-forming element; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic.
 173. A coatingcomposition for use in forming a photocatalytically hydrophilifiablecoating on a substrate, said coating composition comprising: asuspension comprising particles of photocatalytic titania and particlesof silica; said coating composition being capable of forming aphoto-reactive coating comprised of sintered particles of photocatalytictitania and silica upon application on the substrate followed bysintering; said photocatalytic titania rendering upon photoexcitationthe surface of said coating hydrophilic on the order of less than about10° in terms of the contact angle with water.
 174. A coating compositionfor use in forming a photocatalytically hydrophilifiable coating on asubstrate, said coating composition comprising: a suspension comprisingparticles of photocatalytic titania and particles of silica; saidcoating composition being capable of forming a photo-reactive coatingcomprised of sintered particles of photocatalytic titania and silicaupon application on the substrate followed by sintering; saidphotocatalytic titania rendering upon photoexcitation the surface ofsaid coating hydrophilic whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of said coating tothereby prevent the substrate from being fogged or blurred with adherentmoisture condensate and/or water droplets.
 175. A coating compositionfor use in forming a photocatalytically hydrophilifiable coating on asubstrate, said coating composition comprising: a suspension comprisingparticles of photocatalytic titania and particles of silica; saidcoating composition being capable of forming a photo-reactive coatingcomprised of sintered particles of photocatalytic titania and silicaupon application on the substrate followed by sintering; saidphotocatalytic titania rendering upon photoexcitation the surface ofsaid coating hydrophilic whereby adherent deposits and/or contaminantsare away by rainwater as said substrate is subjected to rainfall tothereby permit self-cleaning of the substrate.
 176. A coatingcomposition for use in forming a photocatalytically hydrophilifiablecoating on a substrate, said coating composition comprising: asuspension comprising particles of photocatalytic titania and particlesof silica; said coating composition being capable of forming aphoto-reactive coating comprised of sintered particles of photocatalytictitania and silica upon application on the substrate followed bysintering; said photocatalytic titania rendering upon photoexcitationthe surface of said coating hydrophilic whereby contaminants areprevented from adhering to the surface of the substrate ascontaminant-laden rainwater flows therealong.
 177. A coating compositionfor use in forming a photocatalytically hydrophilifiable coating on asubstrate, said coating composition comprising: a suspension comprisingparticles of photocatalytic titania and particles of silica; saidcoating composition being capable of forming a photo-reactive coatingcomprised of sintered particles of photocatalytic titania and silicaupon application on the substrate followed by sintering; saidphotocatalytic titania rendering upon photoexcitation the surface ofsaid coating hydrophilic whereby deposits and/or contaminants adheringto the surface are released therefrom when soaked in or wetted withwater to thereby facilitate cleansing of the substrate with water. 178.A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a suspension comprising particles of photocatalytic titaniaand particles of silica; said coating composition being capable offorming a photo-reactive coating comprised of sintered particles ofphotocatalytic titania and silica upon application on the substratefollowed by sintering; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of the coating to thereby prevent growth of water droplets. 179.A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a suspension comprising particles of photocatalytic titaniaand particles of silica; said coating composition being capable offorming a photo-reactive coating comprised of sintered particles ofphotocatalytic titania and silica upon application on the substratefollowed by sintering; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentwater droplets are caused to spread over the surface of the coating tothereby promote drying of the substrate after wetted with water.
 180. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a suspension comprising particles of photocatalytic titaniaand particles of tin oxide; said coating composition being capable offorming a photo-reactive coating comprised of sintered particles ofphotocatalytic titania and tin oxide upon application on the substratefollowed by sintering; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic on the order ofless than about 10° in terms of the contact angle with water.
 181. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a suspension comprising particles of photocatalytic titaniaand particles of tin oxide; said coating composition being capable offorming a photo-reactive coating comprised of sintered particles ofphotocatalytic titania and tin oxide upon application on the substratefollowed by sintering; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said coating to thereby prevent the substrate from beingfogged or blurred with adherent moisture condensate and/or waterdroplets.
 182. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a suspension comprising particles ofphotocatalytic titania and particles of tin oxide; said coatingcomposition being capable of forming a photo-reactive coating comprisedof sintered particles of photocatalytic titania and tin oxide uponapplication on the substrate followed by sintering; said photocatalytictitania rendering upon photoexcitation the surface of said coatinghydrophilic whereby adherent deposits and/or contaminants are away byrainwater as said substrate is subjected to rainfall to thereby permitself-cleaning of the substrate.
 183. A coating composition for use informing a photocatalytically hydrophilifiable coating on a substrate,said coating composition comprising: a suspension comprising particlesof photocatalytic titania and particles of tin oxide; said coatingcomposition being capable of forming a photo-reactive coating comprisedof sintered particles of photocatalytic titania and tin oxide uponapplication on the substrate followed by sintering; said photocatalytictitania rendering upon photoexcitation the surface of said coatinghydrophilic whereby contaminants are prevented from adhering to thesurface of the substrate as contaminant-laden rainwater flowstherealong.
 184. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a suspension comprising particles ofphotocatalytic titania and particles of tin oxide; said coatingcomposition being capable of forming a photo-reactive coating comprisedof sintered particles of photocatalytic titania and tin oxide uponapplication on the substrate followed by sintering; said photocatalytictitania rendering upon photoexcitation the surface of said coatinghydrophilic whereby deposits and/or contaminants adhering to the surfaceare released therefrom when soaked in or wetted with water to therebyfacilitate cleansing of the substrate with water.
 185. A coatingcomposition for use in forming a photocatalytically hydrophilifiablecoating on a substrate, said coating composition comprising: asuspension comprising particles of photocatalytic titania and particlesof tin oxide; said coating composition being capable of forming aphoto-reactive coating comprised of sintered particles of photocatalytictitania and tin oxide upon application on the substrate followed bysintering; said photocatalytic titania rendering upon photoexcitationthe surface of said coating hydrophilic whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof the coating to thereby prevent growth of water droplets.
 186. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a suspension comprising particles of photocatalytic titaniaand particles of tin oxide; said coating composition being capable offorming a photo-reactive coating comprised of sintered particles ofphotocatalytic titania and tin oxide upon application on the substratefollowed by sintering; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentwater droplets are caused to spread over the surface of the coating tothereby promote drying of the substrate after wetted with water.
 187. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of tin oxide dispersed in saidfilm-forming element; upon application on the substrate followed bycalcination said coating composition being capable of forming aphoto-reactive coating of photocatalytic titania in which particles oftin oxide are dispersed; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic on the order ofless than about 10° in terms of the contact angle with water.
 188. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of tin oxide dispersed in saidfilm-forming element; upon application on the substrate followed bycalcination said coating composition being capable of forming aphoto-reactive coating of photocatalytic titania in which particles oftin oxide are dispersed; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said coating to thereby prevent the substrate from beingfogged or blurred with adherent moisture condensate and/or waterdroplets.
 189. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous titania and capable of forming a coating of photocatalytictitania upon curing and calcination; and, particles of tin oxidedispersed in said film-forming element; upon application on thesubstrate followed by calcination said coating composition being capableof forming a photo-reactive coating of photocatalytic titania in whichparticles of tin oxide are dispersed; said photocatalytic titaniarendering upon photoexcitation the surface of said coating hydrophilicwhereby adherent deposits and/or contaminants are away by rainwater assaid substrate is subjected to rainfall to thereby permit self-cleaningof the substrate.
 190. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous titania and capable of forming a coating of photocatalytictitania upon curing and calcination; and, particles of tin oxidedispersed in said film-forming element; upon application on thesubstrate followed by calcination said coating composition being capableof forming a photo-reactive coating of photocatalytic titania in whichparticles of tin oxide are dispersed; said photocatalytic titaniarendering upon photoexcitation the surface of said coating hydrophilicwhereby contaminants are prevented from adhering to the surface of thesubstrate as contaminant-laden rainwater flows therealong.
 191. Acoating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising a precursor of amorphoustitania and capable of forming a coating of photocatalytic titania uponcuring and calcination; and, particles of tin oxide dispersed in saidfilm-forming element; upon application on the substrate followed bycalcination said coating composition being capable of forming aphoto-reactive coating of photocatalytic titania in which particles oftin oxide are dispersed; said photocatalytic titania rendering uponphotoexcitation the surface of said coating hydrophilic whereby depositsand/or contaminants adhering to the surface are released therefrom whensoaked in or wetted with water to thereby facilitate cleansing of thesubstrate with water.
 192. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous titania and capable of forming a coating of photocatalytictitania upon curing and calcination; and, particles of tin oxidedispersed in said film-forming element; upon application on thesubstrate followed by calcination said coating composition being capableof forming a photo-reactive coating of photocatalytic titania in whichparticles of tin oxide are dispersed; said photocatalytic titaniarendering upon photoexcitation the surface of said coating hydrophilicwhereby adherent moisture condensate and/or water droplets are caused tospread over the surface of the coating to thereby prevent growth ofwater droplets.
 193. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising a precursor ofamorphous titania and capable of forming a coating of photocatalytictitania upon curing and calcination; and, particles of tin oxidedispersed in said film-forming element; upon application on thesubstrate followed by calcination said coating composition being capableof forming a photo-reactive coating of photocatalytic titania in whichparticles of tin oxide are dispersed; said photocatalytic titaniarendering upon photoexcitation the surface of said coating hydrophilicwhereby adherent water droplets are caused to spread over the surface ofthe coating to thereby promote drying of the substrate after wetted withwater.
 194. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising uncured orpartially cured silicone or a precursor thereof and capable of forming acoating of silicone when cured; and, particles of photocatalytic titaniadispersed in said film-forming element for causing upon photoexcitationthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of the coating to be substituted at least in part withhydroxyl groups in the presence of water under the photocatalytic actionto thereby render the surface of said coating hydrophilic on the orderof less than about 10° in terms of the contact angle with water.
 195. Acoating composition according to claim 194, wherein said particles ofphotocatalytic titania are operable upon photoexcitation to render thesurface of said coating hydrophilic on the order of less than about 5°in terms of the contact angle with water.
 196. A coating composition foruse in forming a photocatalytically hydrophilifiable coating on asubstrate, said coating composition comprising: a film-forming elementcomprising uncured or partially cured silicone or a precursor thereofand capable of forming a coating of silicone when cured; and, particlesof photocatalytic titania dispersed in said film-forming element forcausing upon photoexcitation the organic groups bonded to the siliconatoms of the silicone molecules at the surface of the coating to besubstituted at least in part with hydroxyl groups in the presence ofwater under the photocatalytic action to thereby render the surface ofsaid coating hydrophilic whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of said coating tothereby prevent the substrate from being fogged or blurred with adherentmoisture condensate and/or water droplets.
 197. A coating compositionfor use in forming a photocatalytically hydrophilifiable coating on asubstrate, said coating composition comprising: a film-forming elementcomprising uncured or partially cured silicone or a precursor thereofand capable of forming a coating of silicone when cured; and, particlesof photocatalytic titania dispersed in said film-forming element forcausing upon photoexcitation the organic groups bonded to the siliconatoms of the silicone molecules at the surface of the coating to besubstituted at least in part with hydroxyl groups in the presence ofwater under the photocatalytic action to thereby render the surface ofsaid coating hydrophilic whereby adherent deposits and/or contaminantsare away by rainwater as said substrate is subjected to rainfall tothereby permit self-cleaning of the substrate.
 198. A coatingcomposition for use in forming a photocatalytically hydrophilifiablecoating on a substrate, said coating composition comprising: afilm-forming element comprising uncured or partially cured silicone or aprecursor thereof and capable of forming a coating of silicone whencured; and, particles of photocatalytic titania dispersed in saidfilm-forming element for causing upon photoexcitation the organic groupsbonded to the silicon atoms of the silicone molecules at the surface ofthe coating to be substituted at least in part with hydroxyl groups inthe presence of water under the photocatalytic action to thereby renderthe surface of said coating hydrophilic whereby contaminants areprevented from adhering to the surface of the substrate ascontaminant-laden rainwater flows therealong.
 199. A coating compositionfor use in forming a photocatalytically hydrophilifiable coating on asubstrate, said coating composition comprising: a film-forming elementcomprising uncured or partially cured silicone or a precursor thereofand capable of forming a coating of silicone when cured; and, particlesof photocatalytic titania dispersed in said film-forming element forcausing upon photoexcitation the organic groups bonded to the siliconatoms of the silicone molecules at the surface of the coating to besubstituted at least in part with hydroxyl groups in the presence ofwater under the photocatalytic action to thereby render the surface ofsaid coating hydrophilic whereby deposits and/or contaminants adheringto the surface are released therefrom when soaked in or wetted withwater to thereby facilitate cleansing of the substrate with water. 200.A coating composition for use in forming a photocatalyticallyhydrophilifiable coating on a substrate, said coating compositioncomprising: a film-forming element comprising uncured or partially curedsilicone or a precursor thereof and capable of forming a coating ofsilicone when cured; and, particles of photocatalytic titania dispersedin said film-forming element for causing upon photoexcitation theorganic groups bonded to the silicon atoms of the silicone molecules atthe surface of the coating to be substituted at least in part withhydroxyl groups in the presence of water under the photocatalytic actionto thereby render the surface of said coating hydrophilic wherebyadherent moisture condensate and/or water droplets are caused to spreadover the surface of the coating to thereby prevent growth of waterdroplets.
 201. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising: a film-forming element comprising uncured orpartially cured silicone or a precursor thereof and capable of forming acoating of silicone when cured; and, particles of photocatalytic titaniadispersed in said film-forming element for causing upon photoexcitationthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of the coating to be substituted at least in part withhydroxyl groups in the presence of water under the photocatalytic actionto thereby render the surface of said coating hydrophilic wherebyadherent water droplets are caused to spread over the surface of thecoating to thereby promote drying of the substrate after wetted withwater.
 202. A method for rendering a surface of a substrate hydrophilic,comprising the steps of: (a) preparing a substrate coated with a layerof silicone in which particles of a photocatalyst are uniformlydispersed; (b) subjecting said photocatalyst to photoexcitation so thatthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of said layer are substituted at least in part withhydroxyl groups under the photocatalytic action of said photocatalyst tothereby render the surface of said layer hydrophilic.
 203. A method forrendering a surface of a substrate hydrophilic, comprising the steps of:(a) preparing a substrate coated with a layer of silicone in whichparticles of a photocatalyst are uniformly dispersed; (b) subjectingsaid photocatalyst to photoexcitation so that the organic groups bondedto the silicon atoms of the silicone molecules at the surface of saidlayer are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of said layer hydrophilic until the surface of said layerpresents a water-wettability of less than about 10° in terms of thecontact angle with water.
 204. An antifogging method for preventing atransparent sheet member from being fogged or blurred with adherentmoisture condensate and/or water droplets, said method comprising thesteps of: (a) preparing a transparent sheet member coated with asubstantially transparent layer of silicone in which particles of aphotocatalyst are uniformly dispersed; and, (b) subjecting saidphotocatalyst of said layer to photoexcitation so that the organicgroups bonded to the silicon atoms of the silicone molecules at thesurface of said layer are substituted at least in part with hydroxylgroups under the photocatalytic action of said photocatalyst to therebyrender the surface of said layer hydrophilic whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer.
 205. An antifogging method for preventing a lens frombeing fogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: (a) preparing a lenscoated with a substantially transparent layer of silicone in whichparticles of a photocatalyst are uniformly dispersed; and, (b)subjecting said photocatalyst of said layer to photoexcitation so thatthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of said layer are substituted at least in part withhydroxyl groups under the photocatalytic action of said photocatalyst tothereby render the surface of said layer hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said layer.
 206. An antifogging method for preventing amirror from being fogged or blurred with adherent moisture condensateand/or water droplets, said method comprising the steps of: (a)preparing a mirror coated with a substantially transparent layer ofsilicone in which particles of a photocatalyst are uniformly dispersed;and, (b) subjecting said photocatalyst of said layer to photoexcitationso that the organic groups bonded to the silicon atoms of the siliconemolecules at the surface of said layer are substituted at least in partwith hydroxyl groups under the photocatalytic action of saidphotocatalyst to thereby render the surface of said layer hydrophilicwhereby adherent moisture condensate and/or water droplets are caused tospread over the surface of said layer.
 207. A method for cleaning asubstrate, comprising the steps of: (a) preparing a substrate coatedwith a layer of silicone in which particles of a photocatalyst areuniformly dispersed; (b) disposing said substrate outdoors; (c)subjecting said photocatalyst of said layer to photoexcitation so thatthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of said layer are substituted at least in part withhydroxyl groups under the photocatalytic action of said photocatalystwhereby the surface of said layer is rendered hydrophilic; and, (d)subjecting said substrate to rainfall whereby deposits and/orcontaminants adhering on the surface of said layer are washed away byrainwater.
 208. A method for cleaning a substrate, comprising the stepsof: (a) preparing a substrate coated with a layer of silicone in whichparticles of a photocatalyst are uniformly dispersed; (b) subjectingsaid photocatalyst of said layer to photoexcitation so that the organicgroups bonded to the silicon atoms of the silicone molecules at thesurface of said layer are substituted at least in part with hydroxylgroups under the photocatalytic action of said photocatalyst whereby thesurface of said layer is rendered hydrophilic; and, (c) rinsing saidsubstrate with water whereby organic deposits and/or contaminantsadhering on the surface of said layer are released therefrom and washedaway by water.
 209. A method for cleaning a substrate, comprising thesteps of: (a) preparing a substrate coated with a layer of silicone inwhich particles of a photocatalyst are uniformly dispersed; (b)subjecting said photocatalyst of said layer to photoexcitation so thatthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of said layer are substituted at least in part withhydroxyl groups under the photocatalytic action of said photocatalystwhereby the surface of said layer is rendered hydrophilic; and, (c)causing said substrate soaked in or wetted with water whereby organicdeposits and/or contaminants adhering on the surface of said layer arereleased therefrom.
 210. A method for maintaining a surface of asubstrate disposed outdoors clean, comprising the steps of: (a)preparing a substrate coated with a layer of silicone in which particlesof a photocatalyst are uniformly dispersed; (b) disposing said substrateoutdoors; and, (c) subjecting said photocatalyst of said layer tophotoexcitation so that the organic groups bonded to the silicon atomsof the silicone molecules at the surface of said layer are substitutedat least in part with hydroxyl groups under the photocatalytic action ofsaid photocatalyst to thereby render the surface of said layerhydrophilic whereby contaminants are prevented from adhering to thesurface of said substrate as contaminant-laden rainwater flowstherealong.
 211. A method for preventing growth of water dropletsadhering on a substrate, comprising the steps of: (a) preparing asubstrate coated with a layer of silicone in which particles of aphotocatalyst are uniformly dispersed; (b) subjecting said photocatalystof said layer to photoexcitation so that the organic groups bonded tothe silicon atoms of the silicone molecules at the surface of said layerare substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst whereby the surface of saidlayer is rendered hydrophilic; and, (c) causing adherent moisturecondensate and/or water droplets to spread over the surface of saidlayer.
 212. A method for rendering a surface of a substrate hydrophilic,comprising the steps of: (a) applying onto the surface of said substratea coating composition comprising particles of photocatalyst and afilm-forming element of uncured or partially cured silicone or aprecursor thereof; (b) curing said film-forming element to form asilicone coating in which particles of the photocatalyst are uniformlydispersed; and, (c) subjecting said photocatalyst to photoexcitation sothat the organic groups bonded to the silicon atoms of the siliconemolecules at the surface of said coating are substituted at least inpart with hydroxyl groups under the photocatalytic action of saidphotocatalyst to thereby render the surface of the coating hydrophilic.213. A method according to claim 212, wherein said photocatalyst isphotoexcited until the surface of said coating presents awater-wettability of less than about 10° in terms of the contact anglewith water.
 214. An antifogging method for preventing a transparentsheet member from being fogged or blurred with adherent moisturecondensate and/or water droplets, said method comprising the steps of:(a) preparing a transparent sheet member; (b) applying onto the surfaceof said sheet member a coating composition comprising particles ofphotocatalyst and a film-forming element of uncured or partially curedsilicone or a precursor thereof; (c) curing said film-forming element toform a substantially transparent silicone coating in which particles ofthe photocatalyst are uniformly dispersed; and, (d) subjecting saidphotocatalyst to photoexcitation so that the organic groups bonded tothe silicon atoms of the silicone molecules at the surface of saidcoating are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of the coating hydrophilic whereby adherent moisture condensateand/or water droplets are caused to spread over the surface of thecoating.
 215. An antifogging method for preventing a lens from beingfogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: (a) preparing a lens; (b)applying onto the surface of the lens a coating composition comprisingparticles of photocatalyst and a film-forming element of uncured orpartially cured silicone or a precursor thereof; (c) curing saidfilm-forming element to form a substantially transparent siliconecoating in which particles of the photocatalyst are uniformly dispersed;and, (d) subjecting said photocatalyst to photoexcitation so that theorganic groups bonded to the silicon atoms of the silicone molecules atthe surface of said coating are substituted at least in part withhydroxyl groups under the photocatalytic action of said photocatalyst tothereby render the surface of the coating hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of the coating.
 216. An antifogging method for preventing amirror from being fogged or blurred with adherent moisture condensateand/or water droplets, said method comprising the steps of: (a)preparing a mirror; (b) applying onto the surface of the mirror acoating composition comprising particles of photocatalyst and afilm-forming element of uncured or partially cured silicone or aprecursor thereof; (c) curing said film-forming element to form asubstantially transparent silicone coating in which particles of thephotocatalyst are uniformly dispersed; and, (d) subjecting saidphotocatalyst to photoexcitation so that the organic groups bonded tothe silicon atoms of the silicone molecules at the surface of saidcoating are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of the coating hydrophilic whereby adherent moisture condensateand/or water droplets are caused to spread over the surface of thecoating.
 217. A method for cleaning a substrate, comprising the stepsof: (a) preparing a substrate; (b) applying onto the surface of thesubstrate a coating composition comprising particles of photocatalystand a film-forming element of uncured or partially cured silicone or aprecursor thereof; (c) curing said film-forming element to form asilicone coating in which particles of the photocatalyst are uniformlydispersed; (d) disposing said substrate outdoors; (e) subjecting saidphotocatalyst to photoexcitation so that the organic groups bonded tothe silicon atoms of the silicone molecules at the surface of saidcoating are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of the coating hydrophilic; and, (f) subjecting said substrateto rainfall to thereby permit deposits and/or contaminants adhering onthe surface of said layer to be washed away by rainwater.
 218. A methodfor cleaning a substrate, comprising the steps of: (a) preparing asubstrate; (b) applying onto the surface of said substrate a coatingcomposition comprising particles of photocatalyst and a film-formingelement of uncured or partially cured silicone or a precursor thereof;(c) curing said film-forming element to form a silicone coating in whichparticles of the photocatalyst are uniformly dispersed; (d) subjectingsaid photocatalyst to photoexcitation so that the organic groups bondedto the silicon atoms of the silicone molecules at the surface of saidcoating are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of the coating hydrophilic; and, (e) rinsing said substrate withwater to thereby permit organic deposits and/or contaminants adhering onthe surface of said coating to be released therefrom and washed away bywater.
 219. A method for cleaning a substrate, comprising the steps of:(a) preparing a substrate; (b) applying onto the surface of saidsubstrate a coating composition comprising particles of photocatalystand a film-forming element of uncured or partially cured silicone or aprecursor thereof; (c) curing said film-forming element to form asilicone coating in which particles of the photocatalyst are uniformlydispersed; (d) subjecting said photocatalyst to photoexcitation so thatthe organic groups bonded to the silicon atoms of the silicone moleculesat the surface of said coating are substituted at least in part withhydroxyl groups under the photocatalytic action of said photocatalyst tothereby render the surface of the coating hydrophilic; and, (e) causingsaid substrate soaked in or wetted with water to thereby permit organicdeposits and/or contaminants adhering on the surface of the coating tobe released therefrom.
 220. A method for maintaining a surface of asubstrate disposed outdoors clean, comprising the steps of: (a)preparing a substrate; (b) applying onto the surface of the substrate acoating composition comprising particles of photocatalyst and afilm-forming element of uncured or partially cured silicone or aprecursor thereof; (c) curing said film-forming element to form asilicone coating in which particles of the photocatalyst are uniformlydispersed; (d) disposing said substrate outdoors; and, (e) subjectingsaid photocatalyst to photoexcitation so that the organic groups bondedto the silicon atoms of the silicone molecules at the surface of saidcoating are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of the coating hydrophilic whereby contaminants are preventedfrom adhering to the surface of said substrate as contaminant-ladenrainwater flows therealong.
 221. A method for preventing growth of waterdroplets adhering on a substrate, comprising the steps of: (a) preparinga substrate; (b) applying onto the surface of said substrate a coatingcomposition comprising particles of photocatalyst and a film-formingelement of uncured or partially cured silicone or a precursor thereof;(c) curing said film-forming element to form a silicone coating in whichparticles of the photocatalyst are uniformly dispersed; (d) subjectingsaid photocatalyst to photoexcitation so that the organic groups bondedto the silicon atoms of the silicone molecules at the surface of saidcoating are substituted at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst to thereby render thesurface of the coating hydrophilic; and, (e) causing adherent moisturecondensate and/or water droplets to spread over the surface of saidcoating.
 222. A composite with a hydrophilic surface, comprising: asubstrate having a surface; and, a photocatalytic layer comprised of aphotocatalyst, said photocatalytic layer being bonded to the surface ofsaid substrate; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic such that thesurface presents a water wettability of less than about 10° in terms ofthe contact angle with water.
 223. An antifogging transparent sheetmember comprising: a transparent substrate; and, a substantiallytransparent layer comprised of a photocatalyst and bonded to the surfaceof said substrate; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic such that thesurface of said layer presents a water-wettability of less than about10° in terms of the contact angle with water whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer to thereby prevent the substrate from being fogged orblurred with adherent moisture condensate and/or water droplets.
 224. Anantifogging mirror comprising: a substrate with a reflective coating;and, a substantially transparent layer comprised of a photocatalyst andbonded to the surface of said substrate; said photocatalyst operatingupon photoexcitation thereof to render the surface of said layerhydrophilic such that the surface of said layer presents awater-wettability of less than about 10° in terms of the contact anglewith water whereby adherent moisture condensate and/or water dropletsare caused to spread over the surface of said layer to thereby preventthe substrate from being fogged or blurred with adherent moisturecondensate and/or water droplets.
 225. An antifogging lens comprising: atransparent lens-forming body; and, a substantially transparent layercomprised of a photocatalyst and bonded to the surface of saidlens-forming body; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic such that thesurface of said layer presents a water-wettability of less than about10° in terms of the contact angle with water whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer to thereby prevent the lens-forming body from being foggedor blurred with adherent moisture condensate and/or water droplets. 226.A composite according to claim 222, wherein, for self-cleaning of thecomposite, said layer operates to permit adherent deposits and/orcontaminants to be washed away by rainwater as said composite issubjected to rainfall.
 227. A composite according to claim 222, whereinsaid layer operates to prevent contaminants from adhering to the surfacethereof as contaminant-laden rainwater flows therealong.
 228. Acomposite according to claim 222, wherein, to facilitate cleansing ofthe composite with water, said layer operates to release adherentdeposits and/or contaminants when soaked in or wetted with water.
 229. Acomposite according to claim 222, wherein, for prevention of growth ofwater droplets, said layer operates to cause adherent moisturecondensate and/or water droplets to spread over the surface of saidlayer.
 230. A composite according to claim 222, wherein, to promotedrying of the substrate after wetted with water, said layer operates tocause adherent water droplets to spread over the surface of said layer.231. A composite according to claim 222, wherein the surface of saidlayer is further coated with a hydrophilic protective layer which isoperable to present upon photoexcitation a water-wettability of lessthan about 10° in terms of the contact angle with water.
 232. Acomposite according to claim 222, wherein the surface of said layer isfurther coated with a hydrophilifiable protective layer which isoperable to present upon photoexcitation a water-wettability of lessthan about 10° in terms of the contact angle with water.
 233. Acomposite according to claim 222, wherein said photocatalyst comprisesan oxide selected from the group consisting of TiO₂, ZnO, SnO₂, SrTiO₃,WO₃, Bi₂O₃ and Fe₂O₃.
 234. A composite according to claim 222, whereinsaid photocatalyst comprises the anatase form of titania.
 235. Acomposite according to claim 222, wherein said photocatalyst comprisesthe rutile form of titania.
 236. A composite according to claim 222,wherein said layer further comprises SiO₂ or SnO₂.
 237. A compositeaccording to claim 222, wherein said layer comprises a coating whereinparticles of said photocatalyst are uniformly dispersed.
 238. Acomposite according to claim 222, wherein said layer is made of acoating containing silicone and wherein the surface of said coating isformed of a derivative of silicone in which the organic groups bonded tothe silicon atoms of the silicone molecules have been substituted uponphotoexcitation at least in part with hydroxyl groups under thephotocatalytic action of said photocatalyst.
 239. A composite accordingto claim 222, further comprising an intermediate layer of anon-decomposable material interleaved between said substrate and saidlayer of photocatalyst.
 240. A composite according to claim 222, whereinsaid substrate contains alkaline metal ions and/or alkaline-earth metalions and wherein a thin film for preventing said ions from diffusingfrom said substrate into said layer is interleaved between saidsubstrate and said layer.
 241. A composite according to claim 240,wherein said thin film comprises a thin film of silica.
 242. A compositeaccording to claim 222, wherein the thickness of said layer is less thanabout 0.2 micrometers.
 243. A composite according to claim 222, whereinsaid layer further comprises a metal selected from the group consistingof Ag, Cu and Zn.
 244. A composite according to claim 222, wherein saidlayer further comprises a metal selected from the group consisting ofPt, Pd, Rh, Ru, Os and Ir.
 245. A method for rendering a surface of asubstrate hydrophilic, comprising the steps of: preparing a substratecoated with a layer comprised of a photocatalyst; and, subjecting saidphotocatalyst to photoexcitation until the surface of said layerpresents a water-wettability of less than about 10° in terms of thecontact angle with water.
 246. An antifogging method for preventing atransparent sheet member from being fogged or blurred with adherentmoisture condensate and/or water droplets, said method comprising thesteps of: preparing a transparent sheet member coated with asubstantially transparent layer comprised of a photocatalyst; and,subjecting said photocatalyst to photoexcitation to thereby render thesurface of said layer hydrophilic until the water wettability of saidlayer becomes less than about 10° in terms of the contact angle withwater whereby adherent moisture condensate and/or water droplets arecaused to spread over the surface of said layer.
 247. An antifoggingmethod for preventing a mirror from being fogged or blurred withadherent moisture condensate and/or water droplets, said methodcomprising the steps of: preparing a mirror coated with a substantiallytransparent layer comprised of a photocatalyst; and, subjecting saidphotocatalyst to photoexcitation to thereby render the surface of saidlayer hydrophilic until the water wettability of said layer becomes lessthan about 10° in terms of the contact angle with water whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said layer.
 248. An antifogging method for preventing a lensfrom being fogged or blurred with adherent moisture condensate and/orwater droplets, said method comprising the steps of: preparing a lenscoated with a substantially transparent layer comprised of aphotocatalyst; and, subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the waterwettability of said layer becomes less than about 10° in terms of thecontact angle with water whereby adherent moisture condensate and/orwater droplets are caused to spread over the surface of said layer. 249.A method for cleaning a substrate, comprising the steps of: preparing asubstrate coated with a layer comprised of a photocatalyst; disposingsaid substrate outdoors; subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the water wettability of said layer becomes less than about 10° interms of the contact angle with water; and, subjecting said substrate torainfall whereby deposits and/or contaminants adhering on the surface ofsaid layer are washed away by rainwater.
 250. A method for cleaning asubstrate, comprising the steps of: preparing a substrate coated with alayer comprised of a photocatalyst; subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the water wettability of said layer becomes less than about 10° interms of the contact angle with water; and, rinsing said substrate withwater whereby organic deposits and/or contaminants adhering on thesurface of said layer are released therefrom and washed away by water.251. A method for cleaning a substrate, comprising the steps of:preparing a substrate coated with a layer comprised of a photocatalyst;subjecting said photocatalyst to photoexcitation to thereby render thesurface of said layer hydrophilic until the water wettability of saidlayer becomes less than about 10° in terms of the contact angle withwater; and, causing said substrate soaked in or wetted with waterwhereby organic deposits and/or contaminants adhering on the surface ofsaid layer are released therefrom.
 252. A method for maintaining asurface of a substrate disposed outdoors clean, comprising the steps of:preparing a substrate coated with a layer comprised of a photocatalyst;disposing said substrate outdoors; and, subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the water wettability of said layer becomes less than about 10 interms of the contact angle with water whereby contaminants are preventedfrom adhering to the surface of said substrate as contaminant-ladenrainwater flows therealong.
 253. A method for preventing growth of waterdroplets adhering on a substrate, comprising the steps of: preparing asubstrate coated with a layer comprised of a photocatalyst; subjectingsaid photocatalyst to photoexcitation to thereby render the surface ofsaid layer hydrophilic until the water wettability of said layer becomesless than about 10° in terms of the contact angle with water; and,causing adherent moisture condensate and/or water droplets to spreadover the surface of said layer.
 254. A method according to one of claims245-253, wherein the step of subjecting said photocatalyst tophotoexcitation is carried out with the sunlight.
 255. A methodaccording to one of claims 245-253, wherein the step of subjecting saidphotocatalyst to photoexcitation is carried out with an electric lampselected from the group consisting of fluorescent lamp, incandescentlamp, metal halide lamp, and mercury lamp.
 256. A method for rendering asurface of a substrate hydrophilic, comprising the steps of: coating thesurface of the substrate with a layer comprised of a photocatalyst; and,subjecting said photocatalyst to photoexcitation until the surface ofsaid layer presents a water-wettability of less than about 10° in termsof the contact angle with water.
 257. An antifogging method forpreventing a transparent sheet member from being fogged or blurred withadherent moisture condensate and/or water droplets, said methodcomprising the steps of: preparing a transparent sheet member; coatingthe surface of said transparent sheet member with a substantiallytransparent layer comprised of a photocatalyst; and, subjecting saidphotocatalyst to photoexcitation to thereby render the surface of saidlayer hydrophilic until the surface of said layer presents awater-wettability of less than about 10° in terms of the contact anglewith water whereby adherent moisture condensate and/or water dropletsare caused to spread over the surface of said layer.
 258. An antifoggingmethod for preventing a mirror from being fogged or blurred withadherent moisture condensate and/or water droplets, said methodcomprising the steps of: preparing a mirror; coating the surface of saidmirror with a substantially transparent layer comprised of aphotocatalyst; and, subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 10° interms of the contact angle with water whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer.
 259. An antifogging method for preventing a lens frombeing fogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: preparing a lens; coatingthe surface of said lens with a substantially transparent layercomprised of a photocatalyst; and, subjecting said photocatalyst tophotoexcitation to thereby render the surface of said layer hydrophilicuntil the surface of said layer presents a water-wettability of lessthan about 10° in terms of the contact angle with water whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said layer.
 260. A method for cleaning a substrate,comprising the steps of: preparing a substrate; coating the surface ofsaid substrate with a layer comprised of a photocatalyst; disposing saidsubstrate outdoors; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 10° interms of the contact angle with water; and, subjecting said substrate torainfall whereby deposits and/or contaminants adhering on the surface ofsaid layer are washed away by rainwater.
 261. A method for cleaning asubstrate, comprising the steps of: preparing a substrate; coating thesurface of said substrate with a layer comprised of a photocatalyst;subjecting said photocatalyst to photoexcitation to thereby render thesurface of said layer hydrophilic until the surface of said layerpresents a water-wettability of less than about 10° in terms of thecontact angle with water; and, rinsing said substrate with water wherebyorganic deposits and/or contaminants adhering on the surface of saidlayer are released therefrom and washed away by water.
 262. A method forcleaning a substrate, comprising the steps of: preparing a substrate;coating the surface of said substrate with a layer comprised of aphotocatalyst; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 10° interms of the contact angle with water; and, causing said substratesoaked in or wetted with water whereby organic deposits and/orcontaminants adhering on the surface of said layer are releasedtherefrom.
 263. A method for maintaining a surface of a substratedisposed outdoors clean, comprising the steps of: preparing a substrate;coating the surface of said substrate with a layer comprised of aphotocatalyst; disposing said substrate outdoors; and, subjecting saidphotocatalyst to photoexcitation to thereby render the surface of saidlayer hydrophilic until the surface of said layer presents awater-wettability of less than about 10° in terms of the contact anglewith water whereby contaminants are prevented from adhering to thesurface of said substrate as contaminant-laden rainwater flowstherealong.
 264. A method for preventing growth of water dropletsadhering on a substrate, comprising the steps of: preparing a substrate;coating the surface of said substrate with a layer comprised of aphotocatalyst; subjecting said photocatalyst to photoexcitation tothereby render the surface of said layer hydrophilic until the surfaceof said layer presents a water-wettability of less than about 10° interms of the contact angle with water; and, causing adherent moisturecondensate and/or water droplets to spread over the surface of saidlayer.
 265. A method according to one of claims 256-264, wherein thestep of subjecting said photocatalyst to photoexcitation is carried outwith the sunlight.
 266. A method according to one of claims 256-264,wherein the step of subjecting said photocatalyst to photoexcitation iscarried out with an electric lamp selected from the group consisting offluorescent lamp, incandescent lamp, metal halide lamp, and mercurylamp.
 267. A method of manufacturing a composite with a hydrophilicsurface, comprising the steps of: preparing a substrate having asurface; coating the surface of said substrate with a photo-reactivelayer comprised of a photocatalyst and operable to present uponphotoexcitation a water wettability of less than about 10° in terms ofthe contact angle with water; and, subjecting said photocatalyst tophotoexcitation until the water wettability of said layer becomes lessthan about 10° in terms of the contact angle with water.
 268. A methodof manufacturing an antifogging transparent sheet member, comprising thesteps of: preparing a transparent substrate having a surface; coatingthe surface of said substrate with a substantially transparentphoto-reactive layer comprised of a photocatalyst and operable topresent upon photoexcitation a water wettability of less than about 10°in terms of the contact angle with water; and, subjecting saidphotocatalyst to photoexcitation until the water wettability of saidlayer becomes less than about 10° in terms of the contact angle withwater.
 269. A method of manufacturing a self-cleaning composite,comprising the steps of: preparing a substrate having a surface; coatingthe surface of said substrate with a photo-reactive layer comprised of aphotocatalyst and operable to present upon photoexcitation a waterwettability of less than about 10° in terms of the contact angle withwater; and, subjecting said photocatalyst to photoexcitation until thewater wettability of said layer becomes less than about 10° in terms ofthe contact angle with water.
 270. A method of manufacturing anantifogging mirror, comprising the steps of: preparing a substrate withor without a reflective coating, said substrate having a surface;coating the surface of said substrate with a substantially transparentphoto-reactive layer comprised of a photocatalyst and operable topresent upon photoexcitation a water wettability of less than about 10°in terms of the contact angle with water; forming where necessary areflective coating on the opposite surface of said substrate prior to orsubsequent to or during the course of said step of coating; and,subjecting said photocatalyst to photoexcitation until the waterwettability of said layer becomes less than about 10° in terms of thecontact angle with water.
 271. A method of manufacturing an antifogginglens, comprising the steps of: preparing a lens-forming body having asurface; coating the surface of said body with a substantiallytransparent photo-reactive layer comprised of a photocatalyst andoperable to present upon photoexcitation a water wettability of lessthan about 10° in terms of the contact angle with water; and, subjectingsaid photocatalyst to photoexcitation until the water wettability ofsaid layer becomes less than about 10° in terms of the contact anglewith water.
 272. A method according to one of claims 267-271, whereinsaid step of coating comprises the substeps of: (a) coating the surfacewith a thin film of amorphous titania; and, (b) heating said thin filmat a temperature less than the softening point of the substrate totransform amorphous titania into crystalline titania.
 273. A methodaccording to claim 272, wherein prior to said step of coating thesubstrate is coated with a thin film of silica to prevent alkalinenetwork-modifier ions from diffusing from the substrate into saidphoto-reactive layer.
 274. A method according to claim 272, wherein saidstep (a) is carried out by applying onto the surface a solution of anorganic compound of titanium, followed by subjecting said compound tohydrolysis and dehydration polymerization to form said thin film ofamorphous titania over the surface.
 275. A method according to claim274, wherein said organic compound of titanium is selected from thegroup consisting of an alkoxide of titanium, a chelate of titanium andan acetate of titanium.
 276. A method according to claim 272, whereinsaid step (a) is carried out by applying onto the surface a solution ofan inorganic compound of titanium, followed by subjecting said compoundto hydrolysis and dehydration polymerization to form said thin film ofamorphous titania over the surface.
 277. A method according to claim276, wherein said inorganic compound of titanium is TiCl₄ or Ti(SO₄)₂.278. A method according to claim 272, wherein said step (a) is carriedout by sputtering.
 279. A coating composition for use in forming aphotocatalytically hydrophilifiable coating on a substrate, said coatingcomposition comprising a photocatalyst operable upon photoexcitationthereof to render the surface of said coating hydrophilic on the orderof less than about 10° in terms of the contact angle with water.
 280. Acoating composition according to claim 279, wherein the surface of saidcoating thus rendered hydrophilic upon photoexcitation is operable topermit adherent moisture condensate and/or water droplets to spreadthereover to thereby prevent the substrate from being fogged or blurredwith adherent moisture condensate and/or water droplets.
 281. A coatingcomposition according to claim 279, wherein the surface of said coatingthus rendered hydrophilic upon photoexcitation is operable to permitadherent deposits and/or contaminants to be washed away by rainwater asthe substrate is subjected to rainfall whereby the surface isself-cleaned.
 282. A coating composition according to claim 279, whereinthe surface of said coating thus rendered hydrophilic uponphotoexcitation is operable to prevent contaminants from adhering to thesurface as contaminant-laden rainwater flows therealong.
 283. A coatingcomposition according to claim 279, wherein the surface of said coatingthus rendered hydrophilic upon photoexcitation is operable to releaseadherent deposits and/or contaminants when soaked in or wetted withwater to thereby facilitate cleansing of the substrate with water. 284.A coating composition according to claim 279, wherein the surface ofsaid coating thus rendered hydrophilic upon photoexcitation is operableto permit adherent moisture condensate and/or water droplets to spreadthereover to thereby prevent growth of water droplets.
 285. A coatingcomposition according to claim 279, wherein the surface of said coatingthus rendered hydrophilic upon photoexcitation is operable to permitadherent moisture condensate and/or water droplets to spread thereoverto thereby promote drying of the substrate after wetted with water. 286.An antifogging transparent sheet member comprising: a transparentsubstrate; and, a substantially transparent layer comprised of aphotocatalyst and bonded to the surface of said substrate; saidphotocatalyst operating upon photoexcitation thereof to render thesurface of said layer hydrophilic whereby adherent moisture condensateand/or water droplets are caused to spread over the surface of saidlayer to thereby prevent the substrate from being fogged or blurred withadherent moisture condensate and/or water droplets.
 287. An antifoggingmirror comprising: a substrate with a reflective coating; and, asubstantially transparent layer comprised of a photocatalyticsemiconductor material and bonded to the surface of said substrate; saidphotocatalytic material operating upon photoexcitation thereof to renderthe surface of said layer hydrophilic whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer to thereby prevent the substrate from being fogged orblurred with adherent moisture condensate and/or water droplets.
 288. Anantifogging mirror according to claim 287, wherein said mirror is arearview mirror for a vehicle.
 289. An antifogging lens comprising: atransparent lens-forming body; and, a substantially transparent layercomprised of a photocatalyst and bonded to the surface of saidlens-forming body; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic whereby adherentmoisture condensate and/or water droplets are caused to spread over thesurface of said layer to thereby prevent the lens-forming body frombeing fogged or blurred with adherent moisture condensate and/or waterdroplets.
 290. An antifogging method for preventing a mirror from beingfogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: preparing a mirror coatedwith a substantially transparent layer comprised of a photocatalyst;and, subjecting said photocatalyst to photoexcitation to thereby renderthe surface of said layer hydrophilic whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer.
 291. An antifogging method for preventing a lens frombeing fogged or blurred with adherent moisture condensate and/or waterdroplets, said method comprising the steps of: preparing a lens coatedwith a substantially transparent layer comprised of a photocatalyst;and, subjecting said photocatalyst to photoexcitation to thereby renderthe surface of said layer hydrophilic whereby adherent moisturecondensate and/or water droplets are caused to spread over the surfaceof said layer.
 292. A composite with a hydrophilic surface, comprising:a substrate having a surface; and, a photocatalytic layer comprised of aphotocatalyst, said photocatalytic layer being bonded to the surface ofsaid substrate; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic to permitadherent deposits and/or contaminants to be washed away by rainwater tothereby self-clean the composite as said composite is subjected torainfall.
 293. A composite with a hydrophilic surface, comprising: asubstrate having a surface; and, a photocatalytic layer comprised of aphotocatalyst, said photocatalytic layer being bonded to the surface ofsaid substrate; said photocatalyst operating upon photoexcitationthereof to render the surface of said layer hydrophilic to therebyprevent contaminants from adhering to the surface thereof ascontaminant-laden rainwater flows therealong.
 294. A composite accordingto claim 292 or 293, wherein said substrate is a building material. 295.A composite with a hydrophilic surface, comprising: a substrate; and, alayer comprised of a photocatalyst and bonded to the surface of saidsubstrate; said photocatalyst operating upon photoexcitation thereof torender the surface of said layer hydrophilic to permit adherent depositsand/or contaminants to be released when soaked in or wetted with waterto thereby facilitate cleansing of the substrate with water.
 296. Acomposite with a hydrophilic surface, comprising: a substrate; and, alayer comprised of a photocatalyst and bonded to the surface of saidsubstrate; said photocatalyst operating upon photoexcitation thereof torender the surface of said layer hydrophilic to permit adherent moisturecondensate and/or water droplets to spread thereover to thereby preventgrowth of water droplets.
 297. A composite according to claim 296,wherein said substrate is a radiator fin for a heat exchanger andwherein said layer permits adherent moisture condensate and/or waterdroplets to spread into water film to thereby increase the efficiency ofthe heat exchanger.
 298. A composite with a hydrophilic surface,comprising: a substrate; and, a layer comprised of a photocatalyst andbonded to the surface of said substrate; said photocatalyst operatingupon photoexcitation thereof to render the surface of said layerhydrophilic to permit adherent moisture condensate and/or water dropletsto spread thereover to thereby promote drying of the substrate afterwetted with water.
 299. A composite according to claim 298, wherein saidsubstrate is a surface of an article selected from the group consistingof mirror, lens, sheet glass, and windshield.
 300. A composite accordingto claim 298, wherein said substrate is a surface of a pavement.